Everything which is only supported/needed in the extended version of Party and Friends is written in italic.

What you need to do to get this plugin working:

1. Stop your BungeeCord/Velocity server(s) (multiple BungeeCords are only supported in the Extended version) and your lobby server(s) (or those servers where you want to have the GUI. Party and Friends commands are accessible on every spigot server)
2. Put the jar you downloaded into the plugins folder of BungeeCord/Velocity and into the plugins folder of your lobby server(s).
3. Start your BungeeCord/Velocity server(s).
4. A config.yml was generated on your BungeeCord in plugins/PartyAndFriends. You need to enter your login data of your MySQL server into that config.
5. You should now start the BungeeCord/Velocity and check for errors again. If there is an error look here.
6. Now all commands should be running fine. The BungeeCord/Velocity part (if you have the non-extended version the only part) is ready now. If you want to configure further things you should look at this wiki page, to see how you can change the language for example or use custom message files. All further parts of the configuration are only needed if you have the extended version.
7. ** This step is only needed if you are running a 1.7 - 1.8.3 spigot server (not for 1.8.8 or later): ** Download "Gson for 1.8.3 or older" and put it in the spigot plugin directory.
8. Restart (not reload) all spigot servers where you have installed the GUI on.
9. Now the GUI should also be working.