Partly, you'll want to copy what others are doing. If everyone else only talks for 15 or 20 seconds, then almost anything that you say in a 3-minute monologue will be poorly received. Information that you'll likely want to mention includes: name, department, research interests, possibly where you've just moved from, and maybe a bit about you personally (I enjoy triathlons; married with two kids; active in a barbershop quartet; etc.) One point about your research interests: keep it very nontechnical. Rather than give many details, say something like I write computer programs to help blind people use computers, or I study 18th century literature, particularly the works of SoandSo. Most likely, this activity will be pretty informal. If you're still a little nervous about it, you might ask another junior faculty member in your department.