This is a guide outlining the strengths and weakness of certain guns, and also good ways to use each gun effectively. This guide only focuses on the weapons commonly used in competition for the Counter-Strike games. If the weapon is not listed in this guide, you probably don't want to use it in your match or scrim.
M4A1 (M4) guide
AK47 (AK) guide
Desert Eagle guide
Read the Counter-Terrorist Guide
Read the Match/Scrim Guide