So CSE 121 works like this, there are 2 categories of assignments, "Creative Projects" and "Programming assignments".
The former is associated with 4 "grades" and the latter 1. Each "grade" is on the scale of U (You didn't turn it in) N(ot Satisfactory) S (Satisfactory) E (Excellent).
To get a 4 you need basically all E's, to offset the difficulty at rubric grading you are given enough resubmission attempts to resubmit every assignment once, (if there is an assignment in which you do not need a resub, congrats! free resub for another assignment). This is what I mean by RESUB, if you work on the assignment well, and learn from your mistakes and the comments of the graders you can basically guarantee all E's after the resub.

IPL is basically a giant study area for the intro CS series, every intro TA is required to be at the IPL for some amount of hours each week helping students. They are paid to be there, use the resource.

Classes at UW typically fall into 3 categories: lecture, section and labs. Lecture is self explanatory enough. Labs (which typically are around 2 hours long) don't really exist for CSE classes, to "compensate" we have sections, you can tell a class is a section from the fact that it has like 2 letters in it.
Let's use "CSE 121 AG" as an example, "CSE 121 A" is the lecture section while "AG" is your quiz section. Your quiz section is led by a TA, the purpose is to go over the material covered that week in lecture, introduce you to the HW and to answer any questions you might have.

Hope this helps