How to play with friends in my single player worlds? [duplicate]

If you two are in the same building/connected to the same network:

To start, you'll want to make sure that both you and your sister are playing on computers that are:

• Connected to the Internet, so that the game may launch in Online mode
• Connected to the same network, so that the computers may find and connect to each other
• Running the same version of Minecraft

Next, you'll both need to sign into your Minecraft accounts. Now, since you're the one hosting, you will need to do as follows:

• Open the world
• Go to the pause menu (default key is ESC)
• Select the "Open to LAN" option
• Configure settings for the world as you wish (default game mode and whether cheats are allowed for other players or not)
• Finally, press the "Start LAN server" button, which is usually located in the bottom left-hand corner.

To close the LAN server, simply exit the world.

If you two are not connected to the same network (not in the same building, etc.):

There are a fair number of ways to set up a multiplayer server. In you're case, we're looking to start a server which only people who are connected to a certain virtual network may connect to. I've found that one of the most widely used ways to accomplish this is by creating a Virtual Private Network (VPN) using a free utility called LogMeIn Hamachi.

The first order of business is to install Hamachi and get the MC server executable, the latter of which may be found here. If your computer is running Windows and you just want to get the server setup, you can download the file "minecraft_server.1.8.1.exe". Otherwise, Minecraft.net provides a short and sweet tutorial for running a command-line server using the "minecraft_server.1.8.1".jar" file. Download either the executable or the JAR, or both if you want to try each one. We'll get back to this file later.

Now, a word on getting the LogMeIn Hamachi tool. First off, you'll want to create a LogMeIn ID (pretty much an account on their site) -- but we all know how to do that, so I'll move on. After you're done with that, you'll want to actually download Hamachi, which can be done at this page. (Note - select the 'Unmanaged' option.) The installation wizard will then guide you through installation of the program. Once the installer has finished, you should be presented with a window similar to this:

Make note that Hamachi must be installed on all computers which will be connecting in order for this to work.

Click the "Power" button in the top-left corner and the program should display an IP address next to this button. This will be crucial to other players' ability to connect to the server later.

Now, assuming you will be hosting the server, you will want to follow these steps. In the Hamachi window, navigate to the 'Network' option on the toolbar. Open its drop-down, and select "Create a new network...". You will then be prompted to enter a name and password for your network. Obviously, you will want to make note of this info as your clients will need it to connect to the VPN, so do so as you enter in the network's info. Congrats, you've just created your Hamachi network. There may only be a certain number of clients (including yourself) in the network, but this will most likely not be an issue in your case.

The next step is to have your client(s) get Hamachi and connect to your network. Have them create their account and download the program as I described above. Then, what they will need to do is navigate to the Network tab and select "Join an existing network...". They will be prompted to enter the network's name and password, which we are assuming are supplied by you. If you two have followed this procedure correctly, your sister should now be connected to your VPN.

Now, for the actual server. It is recommended that you place the server executable inside its own folder, as it downloads the server files to the same directory as itself. You will next need to run the server executable -- for this tutorial, we'll go with the EXE file. Simply double-click the file to run it and start the server. Make sure to leave this program running! Depending on your computer, you may or may not have enough resources to be able to simultaneously run the server and your Minecraft client at the same time, which could cause problems.

By now, your Hamachi network should be up with you and your sister connected to it, and the Minecraft server should be running. If you want, you can mess around with the server options in the server.properties file using any text editor (e.g. Notepad).

Remember the IP address next to the Power button on your Hamachi window? Now is when that comes in. First off, copy the address into your clipboard. In Minecraft, from the main menu, navigate to the Multiplayer menu. I have read that your server might show up as a local game. If this is not the case, select "Direct Connect" and connect using the address you just copied. Don't forget to give the IP to your sister so that she can connect!

Alright! Now, if everything has worked out fine, you and your sister should be connected to your own private Minecraft server. From the server executable window, you can do things such as op and de-op players, change the time, and basically use all of Minecraft's commands (plus a few others, if I'm correct).

By now, you should be able to play Minecraft with your sister on a private server, whether local or long-distance! If anyone has feedback or constructive criticism relating to this answer, I'm all ears. Have a nice day, everyone.