Depending on the field that you are interested in, the nature of the research can very different. I think for the humanity ones tend to be the library type, while the science ones are more hands-on and working in labs. I don't know too much about researches in the humanities, but for the sciences in general, you can do research both during the school year and over the summer. During the school year, you can do research for credit, and it can count up to one full class credit. I believe you can also do it for pay, but that you have to talk to the specific professor/department. As for summer research, you apply for grants. The most common one is Summer Undergraduate Research Program [SURP]. Then there are grants that are specific to departments or fields. Note that SURP and other grants apply to the humanity researches as well. So this year, Pomona is giving research grants over 120 students for summer research:
Pomona College : News@Pomona. In fact, I am currently staying on campus for 10 weeks to do chemistry research in the lab. I am an upcoming-sophomore, and I started working last semester. I have friends who are in similar situation, so it is possible for freshmen to start doing research, especially in the science fields. Someone else can offer more information for the humanity researches. I hope this helps.