Download and extract Project64K to a folder on you computer (i.e. C:\PJ64K)
Then create a folder for your roms (i.e. C:\N64roms)
Now go to the folder where you extracted Project64K and double-click on project64k.exe to open it.
Now go to File>Choose Rom Directory and select the folder where you're going to put your N64 roms in and click ok.
Everytime your add or remove roms from that directory go to File>Refresh Rom List and any roms added/removed from the directory will be added/removed from the rom list.
Now you may want to configure your controls. Go to Options>Configure Controller Plugin
Next, go to File>Start NetPlay and the Kaillera netclient will come up. The tabs above are self explanitory. Where it says username enter your desired nickname. Kaillera should start pinging servers. You want a server with a low ping. The lower the better. To enter the server double-click on it.
When you enter the room you can talk by typing in the skinny middle box and pressing enter. You can create a game by clicking the button Create New Game and selecting your game or you can join a game by clicking on the game in the bottom box and then clicking the Join button.
If you created a game people will join and you can kick people by pressing the Kick button which is useful for irratating people, campers, and for people with very high ping. You can talk by typing in the bottom box and pressing enter. To play press the Start Game button and the game will start. To drop out of the game while its playing go to File>End Emulation. And finally, to exit your created room press the Cancel button.
If you join a game you can talk by typing in the bottom box and pressing enter. You can leave the room by pressing the Leave button. The game will start when the host starts the game. To drop out while the game is playing go to File>End Emulation.
To talk while in a game press Ctrl+M on your keyboard, type in what you want to say and press Enter.
That wraps up the tutorial. Have fun :)