:bash: What do i do to start with? :bump: 
Help
First and for all: look for the all-mighty
Search button.
It’s now 2 times on this page, so look for the other one. 
Second: sit down for a while and ask yourself what to search for. What do you want to do?
Do a lame quick-mod just by replacing some textures or sounds?
Going some more exotic by modifying game models?
Or do the real freaky (but most flexible) stuff by messing with the code?
What do you want to change?
Do you want to replace sounds?
Or add voicechat sounds (needs a little bit of scripting)?
Or add new sounds (needs coding)?
As far as I remember this one is for creating additional voicechats:
Custom Voice Chats
And this one is for replacing assets in general:
Basic “how to make a graphic / sound mod” tutorial
It’s also a good idea to take a look at existing mods.