Possible Duplicate:
User’s Guide vs Users’ Guide
As in, a conference that is for people in their first year of, say, University.
Possible Duplicate:
User’s Guide vs Users’ Guide
As in, a conference that is for people in their first year of, say, University.
Those in their first year at a university are commonly called first years. Thus, their conference would be first years' conference.
The conference is held annually, so there's only one first year for a year. You should use "first year's".