I would recommend that you would view some online tutorials.

You can also look in free models and have a look at the code.

 

Also, in roblox studio. There is a tab called the object browser. That will tell you about anything.

 

It's in alphabetical order and you can use your keyboard to navigate, similar to a dictonary but for LUA scripts.

 

A good start would be this series: Beginner Series

 

Once you have learned the basics. You can attempt to make your own game or use this series

to make a game that's more mature.. you can do a simulator if you want though.

 

Make a doors game: Doors

Make a simulator: Simulator

(simulator tutorial is a bit cringe lol)

 

After that, go make games.. or exploits. I honestly don't care about the end result.

You do not need to focus on Terrain if your wanting to learn coding.