Second year grads help the department by taking on one of these roles. You'll be contacted by the student faculty reps at the end of your first year in the program, to provide your preference on which role you'd prefer. Assignments will be made in June or July. Please see the list below, including descriptions from past grads in these roles.

Recruitment coordinators (3-5 grads, although all second years help with recruiting)
Responsibilities include coordinating social events, housing tours, and other such activities for Sunday; helping the applicants to find their interviews and keep them on schedule on Monday; and hanging out with them for lunch and dinner on Monday. You should be willing to drive a University car or van around (or recruit one of your colleagues to do this), and charge lunches or dinners to your credit card and await reimbursement. Most importantly, you should be excited about the department and eager to attract prospective students here. This job is really fun, and as you'll be involved anyway, it's a good way to get credit for it.

Retreat coordinators (2-4 grads, although all second years help with the retreat) 
This job includes arranging introductions for the faculty, introducing the new first years, and organizing a fun game night. Like recruitment, this job is everyone's responsibility so you're just the point-people to make sure the student side of things gets done. 

Community / social media coordinator (1 grad)
The Community / Social Media Coordinator will serve as MC for first year rotation talks at the end of each quarter and organize an annual departmental event of their choice (e.g. bakeoff, etc) with admin staff support.  Will also assist with selecting items to post to the department website, X account, and LinkedIn account by canvassing labs for awards, papers, and other things to publicize once or twice per quarter.

Student Leadership Council / Faculty rep (2-3 grads)
Council members are responsible for attending all the faculty meetings and representing the interests of the graduate students. Faculty meetings vary; some have a lot of items to discuss and others have less. This job is a really interesting chance to see some of the inner workings of the department and get to know faculty. You should be willing to join the discussion when issues of relevance to the graduate students come up. You need to be willing to solicit feedback from students and make brief presentations at the faculty meetings as appropriate. You also should be willing to write timely email summaries of all of the meetings. Council members also organize some orientation events and the mentor program for the incoming first years.