What are support duties in LoL compared to DotA?

Basically supports are enablers for the carry. The support will ward to prevent ganks, and depending on the lane matchup either help harass the enemy or play defensively. Of course each support has different strengths and weaknesses so these are just general things most if not all supports would do. Some supports can be played both offensively and defensively, but it depends on which champions are being played and what they can do. If both lanes are playing defensive then yes it can get stale. You might look to start a fight if possible, otherwise just hang around and let your carry farm up.

As for your questions on the jungle, the camps are way too strong for a support to take. The crab in the river, while not dealing damage, has a lot of hp and resists so as a support it will take a long time to kill. This will either leave your carry open to being killed 2v1 in lane, or the enemy jungler could find and kill you as well. Generally supports will not roam to other lanes for the same reason, but you can roam if the time is right. Any time where your adc is not at risk you could look for a gank opportunity. If your lane opponents are both away or your adc is in base would be good times for a roam.

The very reason there is a duo lane bottom is to keep early pressure on dragon. So keeping the river and/or dragon pit warded both reveals possible ganks and prevents the enemy from sneaking in a dragon kill. This also goes for baron in the mid to late game after laning phase is over. You might be surprised how often people neglect to keep track of neutral objectives. Having someone on the team to give guidance can help keep everyone on the same page.

So general laning duties would be:

• Warding against ganks
• Harassing in offensive matchup
• Healing and/or shielding in defensive matchup
• Help keep time on dragon

Once towers start falling the laning phase is over or soon will be. You should have a sightstone by now, and a red sweeper trinket. While everyone on the team can help with vision, the support has the most tools to contribute. While you aren't warding you should be sticking with your team. What you do then will largely depend on the champion you play. So again just general rules to apply.

Mid to late game focus switches to:

• Keeping up your vision control
• Removing the enemy's vision
• Help guide the team on what objectives to focus
• Being with your team to help in fights

Should I try killing the little creature near baron for vision and speed or leave that to jungler?

No, the scuttle will take you forever to kill, leave it to the jungler for two reasons. One they kill it faster with the bonus damage of the machete. and two they get bonus gold and even bonus damage if they have devourer.

is it ok to try to lead as support in public game by helping jungler with timing or the timing in general with mentioning if dragon will be soon etc.

Yes this is a good thing to do. Your other 4 team members are focusing on getting their minions so you can provide them support by watching for mia's, pointing out where the jungler is and warning about roams and ganks.

Can I go kill some neutrals in forest on my own or it's bad idea and jungler would hate me?

Depending on what support you're playing you may not be able to. If you can then it's probably only worth it for Golems, but note where your jungler is and where he's going. If he just cleared blue and is at wraiths (raptors) then you probably shouldn't as they will likely be planning to take red and then Golems. Just be mindful of the jungler when you do this. But again there aren't too many supports that can easily take it. The time and health cost may be too great for it to be worth it. You'd likely make more gold using the support items gold gaining ability.

Lots of good answers here, but wanted to add a few things that might not be clear from them and/or from the change in games (or just to new players in general).

• It's noteworthy that even being around things when being killed (minions and neutrals) shares XP. So it might be easy/tempting to "help" a jungler kill things but they also may not like it since you may be taking xp away from them. That being said if your carry is comfortable being in lane by themself, you roaming away to help support ganks/drop wards/etc can give them extra xp by your absence. UPDATE: They changed it since I posted this that the killer of the jungle mob gets full xp, it's no longer shared.
• I think another thing you can do as a melee support (ranged are a little more risky but can also do it) in lane is "screen" vs enemies, basically standing in between your enemies and your carry, so they have to go through you to get to them. This is dangerous for you but it definitely keeps you from being bored (unless you're dead=}) as you need to be ready to back off/run at quicker notice. It also puts you closer to the enemy if you have a chance to engage. Note, some carry might feel like you're getting in the way when you do this as well.
• As far as warding, while everyone starts with a trinket ward, you can update the support items to allow more wards which make the support a more capable warder. Example: http://leagueoflegends.wikia.com/wiki/Eye_of_the_Watchers. Getting more/good wards out there also allows other to change to other trinkets if they wish. While this may not be for everyone the build paths are such that you almost never see anyone but support and occasionally jungler buying these items.
• If particularly antsy in lane, http://leagueoflegends.wikia.com/wiki/Relic_Shield does allow some killing of minions while contributing back to your carry. It also gives you another thing to watch (recharges). I find this item very useful playing supports which have no heal before your carry gets his lifesteal really going.
• In mid-late game, active items like http://leagueoflegends.wikia.com/wiki/Mikael%27s_Crucible give you something else to be ready to do if chaos ensues.

Disclaimer: I've never played Dota so sorry if any of this is obvious=) I'm not Diamond 10 or anything in League but the role I play most is support. Also watch a lot of eSports and what "the pros do" (which I highly recommend if that kind of thing is fun to you).

The main objective as playing support is to be useful while not participating in farming.

In game there are 4 sources of farm, which is top,mid,bottom and jungle, but there are 5 characters. Back in the season 1 of league of legends, people figured that having 4 full farmed champions and one without farm is better than having 5 players farming 4 sources. So fifth champion, was titled as "support" and consisted of champion picks that may be effective with very little gold.

For your duties:

Always: Warding map to prevent ganking/taking dragon and dewarding enemies.

For first phase of game ("lane phase"): Stay with your adc on lane and help him as much as possible - control the map and warn him about ganks, poke enemies, engage on enemies, defend him if you are ganked, save him if enemies are about to kill him. If you have winning lane (eg. Leona/Lucian vs Nami/Vayne) then try to find positioning mistake and engage for kill or try to zone them out of farm by providing a threat. If you have losing lane, try to disengage enemies and defend your ad carry. If both lanes are near to equally strong, sometimes you will be just rightclicking on floor watching as your and enemy adc both passively farming.

On the final phase of game ("teamfight phase"): Either try to make good engage vs enemy team (with leona,blizcrank,alistar,thresh,nami) or try to distrurb enemy team (sona, janna, nami, tahm kench) by doing as much mess as possible or try to defend your ad carry (called "peeling"). Unless some of enemies are superfed, your ad carry is best source of teamfight damage with constant fire rate (without cooldown) and high damage, but at the cost of being oneshotter for everyone. If your adc manages to have good damage in teamfight, protect him stunning, knocking away enemies, healing him, shielding him etc.