How do i install gmod and what i need to buy!

Hey i’m new at GMOD,

And i want to play Roleplay servers but i don’t know what i need to buy.
Because you got like GMOD + Counter strike source our Half life 2.
What you need to buy in order to make GMOD run on roleplay servers?

Regard, Niels

Most RP servers need CSS

Yes, buy the CS:S + Gmod package in Steam and save $5. That’s what I did.

Aah cool going to buy it now