Math-U-See is a program that is "mastery" oriented. That means that you don't move forward until your student masters the concept you're working on.
So ... practically that means that you'll cover about one lesson per week. But that can change ... you can spend longer if your student doesn't quite "get" a concept, or you can move more quickly if your student grasps a concept easily.
The video is designed for you and your student to watch together.
The worksheets are really for you to decide. They help to reinforce the concepts being taught. So if you find your student struggling over a specific lesson, you may wish to use all the worksheets. But if your student breezes through a lesson, you may decide not to use any!
I do believe that once you "wade in", you'll find that it isn't all that confusing. You and your student will learn together how to best use the materials offered.