When on an offensive security team, there are different levels of engagement that you will have, as well as different sets of rules you must follow, sometimes from engagement to engagement. Of those, one of the most common you will face is a simple Vulnerability assessment. This is little more than testing for the presence of a vulnerability. Sometimes its for a popular vulnerability that is trending in the news, or for an outdated server that reported poorly on the last vulnerability scan. Either way, they are quick, easy, but tedious and tend to have plenty of paperwork to go along with them.
The other type of tasks will be a full penetration test. Some times its a white box test with full knowledge of your target, as well as the target having full knowledge of you. Other times it will be a black box stealth mission to see how badly you can compromise your target.