Here's a quick informative sheet to get you up to speed with FiveM development.
ScRT means Scripting Runtime or Script Runtime. FiveM has three different scripting runtimes available (Lua, C# and JavaScript), and they are mentioned down below.
The scripting manual can be found here and it features the following articles:
You can refer to the page mentioned above to see the scripting manual in full detail.
Simply put, a Native, is a function exposed by the game in order to be called from scripts and either perform a given action in the game itself or request data from it. For example, one would type the following, to get the local player's ped from a Lua script and then give a weapon to that ped.
ped = GetPlayerPed(-1)
GiveWeaponToPed(ped, GetHashKey("WEAPON_PISTOL"), 100, false, false) -- We got a gun now!
Natives are located here.
Developer commands can be found here.
These are named Game references, and they can be found over here.
Hitch warnings indicate that one of your resources is not performing as it should and you should look into the affected resource to figure out why, using the profiler can help diagnosing this. Things such as these, can sometimes be caused by writing underperforming SQL queries that take a long time to execute, as well as unoptimized loops that end up halting the script execution.
The profiler can be used to diagnose why a resource is taking a long time to execute, there's a guide explaining how to use it, it can be used both on the server and client.
The resource monitor can be used on the client to diagnose which resource is taking a long time to execute, it shows certain things such as cpu usage (msec) and memory usage for each resource.
It can be enabled by typing resmon true. It's possible that you see a message such as Access denied for command resmon (especially when running in production builds), this means that the developer mode needs to be enabled by launching the FiveM/RedM client using the +set moo 31337 argument (for example, by adding it to a shortcut).