How to get weapons other than a pistol in-game:

> Press B

How do I plant/defuse the bomb?

> Hold F

What is the yellow thing on the wall?

> It is a reinforced wall (placed by defenders, ALSO BY ATTACKERS), which means you need two C4s to destroy it.
> If it's just a brick wall, you can destroy it with a single C4
> If it's a wooden wall, you can shoot through it like in R6S, possibly to create a rotation to the site or to surprise the enemy.