1- You must own a legal copy of GTA V
2- Download the client here: Fivem.net and click on download client
3- Download the Client into a folder, because all the files will be installed where that Fivem.exe is downloaded at. So be sure to create a folder for it.
4- After downloading it and installing it, launch it and in the server browser type RelaxedRP, and click on it then connect.
5- If it doesn’t appear within the in game browser, sometimes the in-game browser can be funky and use the following link and type RelaxedRP in that browser here: FiveM Browser Server Browser
6- Joining the RelaxedRP Server for the first time will take a while… there are a LOT of files to download, you can read the details at the bottom right of the Loading Screen.
7- You may want to reconnect a couple of times to the server to ensure that you have cached all the files correctly for the best playing experience. To quit the fatest way and cleanly from FiveM, hit F8 while in game, that will open a console, then type quit in that console and hit enter.
8- After that, you’re on your own. Best to follow the New Player Guide to get you on your feet and learn how the Mechanics of a FiveM server works, as it is different than Single Player and GTA Online. Be sure to browse this website fully to make sure you understand everything. A lot of information is there for you for this purpose.