I need help making my first gamemode!

Hi, first of all, what program (or whatever) do you use to make the gamemode, and second of all how do you make it? I am a noob at LUA,coding,etc so a helping hand would be aprieciated<(dont blame my spelling).
The type of gamemode im going to make is called “Bull Run”, it is where players start off at a specific area with lots of antilion guards behind them, if they get caught/killed then they are out and the game will end when either everyone alive makes it to the end or when everyone has died.
If possible could anyone give me a link to (or make a tutorial) on how to make a gamemode.

Read the other pages on the gmod wiki aswell.

Thanks ill look at it now.