Spartan Ops are a type of mini mission where you have to complete a few objectives and kill the covenant and Prometheans.
From the Main Menu, click on Infinity, then Spartan Ops, the select a episode you wish to play, then the chapter, and which ever difficulty you wish to attempt.
The missions are pretty straight forward and there is not much to explain to complete them. You do not have to worry about dieing since you seem to have an infinite amount of respawns. This achievement can be done solo or cooperatively. Once you complete one of the chapters, you will earn this achievement for an easy 15G