what’s the best way of getting a work when you are an undergrad?

I would have said your school’s career center should have job postings but if you are not going to school, the usual channels- such as looking in the paper or job websites, even craigs list. Talk to people you know to see if there are any openings where they work. Believe it or not, many employers, depending on the type of work and size of the company would just as soon interview someone on a personal recommendation than go through the process and hassle of posting a job opening and dealing with a bunch of people- it is very time consuming.