Useful guides
How to install skins for CSS v34
Installing skins for v34

Skin installation for CS:Source v34 explained

How to install skins for CSS Steam
Installing skins for v92

How to properly install skins for CS:Source v92+

Switch to right hand in CSS
Left hand fix

How to fix left handed weapons in Counter Strike: Source explained

Page 18 - M4A1 for Counter-Strike: Source