i am currently learning remote function and remote events and i need to know this.
Either.
I think I answered your other question in relation to showing a GUI to just one player, so I'll just quickly explain
The client can not make changes to the server, so if we were to have a GUI that, when clicked, spawns a car, we'd have to use a RemoteEvent since the client (AKA the player who clicked the GUI) can not change the server (by inserting a car into the workspace).
This is where RemoteEvents come in.
We can use a RemoteEvent as a sort of way to "message" the server and then it gets decided on the server side how to handle these events.
This was introduced into ROBLOX as a way to stop hackers by changing it so the hackers can only see their hacks, no one else.
If you have any other questions I'd happily answer those too.
Hope this helped!