Most students enroll for 1 or 2 credits the first semester that they are involved in research. Make sure that you have enough time to do research and that you are really interested in research. Later on you can enroll for more credits. If you are an Arts and Sciences students there is a maximum of 6 credit hours per semester with one professor and 8 with more than 1 professor. Students in the College of Agriculture and Life Sciences may count 15 credits of research towards graduation.
Every professor has different expectations of undergraduate research students.
Ask them what will be required of you at the end of the term. Most professors require either a written or an oral summary of your progress for the semester. Again, every professor has ideas about the number of hours that you need to work in the lab to get one hour of credit. The rule of thumb is that students receive one hour of credit for every 3-5 hours per week they spend working in the lab, with the minimum being three hours per week per credit. Talk to your research advisor.