I've been really confused of when to use remotes. A reply would do a lot
Say you have a shop GUI and leaderstats of money, and the player clicks to own something and it costs $5000, if you take away 5000 on the client, it will only show for the client, not the server, so you have to fire a remote event to the server to tell it to update
Remote events are used to access the server from the client or the other way around.
Client means the game that is running on your device, the server is the place where the clients are running.
For instance, if I want to change something on the server using a local script, I should use Remote events/functions. The client can access the server through them.