it is my first time ever playing gta RP and it seems that most things aren’t loaded in properly, for example I cannot see any other players at all and some parts of the map don’t have any floor at all
Most likely it’s because you joined heavily modified server, using too many custom assets and your FiveM client need some time to download them all first. Hence you’re not being able to see players (custom body part, clothing etc.)
After opening main FiveM menu, go to settings (top right), “Game” and check this box. This will tell you how much you need to download upon joining each server in order to see everything correctly.
Note you’re client streams in only what’s in your area and some additional downloading of assets on a fly will be needed as soon as new content will be shown to your FiveM client. Meaning, you might load in a ton of stuff in the city, but when going country side, you might need to wait once more everything from there will stream in for the first time too.
All while I presume you joined a server that’s modified correctly and is not simply bugged out beyond repair. That also happens.
That happens due to custom assets, just wait for them to load - the amount of time it takes varies greatly depending on the bandwidth of both your PC and the server you are playing on, among a few other things. If you wish to track the download progress you can enable the setting for it in the FiveM launcher settings page (top-right cog icon).