Tsk tsk tsk Partninja, page references...
For assaulting a building / fortification, the rules can be found on page page 94 under Grenades, with regards to battlements you can find that on page 96 in the second paragraph under Assaulting the battlements.
For assaulting vehicles you can find the rules on page 76 under fighting the assault, and use those rules in conjunction with the rules for grenades on page 61 in the third paragraph under grenades, beneath the subheading of vehicles and monstrous creatures.
When it comes to the shooting phase, follow the rules on page 61 in the first paragraph under grenades.