How exactly do I install Minecraft Mods and what is Forge?

Minecraft Forge is a modding API (Application Programming Interface), which makes it easier to create mods, and also make sure mods are compatible with each other.

The method that you are trying to use, by deleting META-INF and placing the files is not the way to install mods anymore. The new Minecraft launcher prevents modification of the actual game files, because it simply re-downloads them if they have changed.

Instead, you can create a new 'profile' in the Minecraft launcher containing the modified game file, preventing the launcher from refreshing the files. Forge actually comes with an automatic installer, which does this for you.

You can find the downloads for the automatic installer here. Find the link called 'Installer' beside '1.6.4-Recommended' (If you are on Windows, use the link called 'Win-Installer'), and download it (wait 3 seconds and then click 'SKIP AD' in the top right in the opened window). You can then run the downloaded file.

In the installer, make sure that the 'Install Client' option is selected, and then select 'OK'. Forge will now download and install. To make sure Forge is working and let it setup any extra files, open the Minecraft Launcher, and in the bottom left, click the dropdown beside 'Profile:' and select 'Forge'. Then, click Play to begin. If, in Minecraft's menu, you see a Mods button, then Forge is ready to go!

To install your mod, copy all of the files in the LifeInTheWoods.zip file into the new .minecraft/mods folder, run the game, and viola!

I think you should accept one of the other answers, I've added this as an answer as it started getting a bit long for a comment!

This last weekend I've been installing mods for the first time (for my son, you understand). I found MultiMC to be very useful tool for this, let me explain.

When you bought Minecraft you also got the right to download and play all the earlier versions of it.

First thing to know is that mods are written with a specific Minecraft version in mind. Commonly the versions of Minecraft targeted are 1.7.2 or 1.6.4 (notice this is not the latest Minecraft - which at the time of writing is 1.7.9).

Second thing to note is that you need a different version of the Minecraft Forge to work on the different Minecraft versions. Forge is used to load the mods.

So it won't take long before you'll need some way to manage having multiple versions of Minecraft and Forge and all the mods. This is where MultiMC comes in very handy.

MultiMC allows you to manage multiple versions of Minecraft, Forge and the various mods involved. Sign in with your Minecraft account details and with a couple of clicks it can download various Minecraft versions and the corresponding version of Forge. I already have numerous 1.7.2 and 1.6.4 instances (Unlimited Superheroes, Fossils and Archeology, Tekkit etc.). Also this allows you to experiment with combining different mods together to check to see if they crash - you also might want to keep your differently themed mods apart. You can also organize your saves (e.g. world maps) and resource packs across the various instances (e.g. city maps and textures for use with the "cars and drives mod")

Alternatively if you find MultiMC a little too heavyweight you could always try using the Technic Launcher first which looks to do a similar job to MultiMC (without as much obvious configuration). I also found I could copy the mods I downloaded with the Technic Launcher into my MultiMC managed folders!

Well if you havent got it yet first make sure you got the forge INSTALLER. Next run normal minecraft on the version your modding then make a world and exit minecraft. then click on the forge installer and install client next go into the minecraft launcher and change your virsion the the forge [should be at the bottom and run it then when it stats exit it lastly open your .minecraft folder look for mods and drag the mod into the folder i hope this helps you i had problems to when i started moding good luck