A CV is your Curriculum Vitae....it is your academic resume. It shows all of the labs you've worked in, related places of employment, degrees earned, honors and awards you've earned, and poster presentations and/or publications you've gotten. There are lots of websites out there that can help you write and hone your CV.
A poster presentation is exactly what it sounds like. If a person has been working on a research study, they can submit the findings to research conferences in the forms of either oral presentations, where you present your study for 10 min or so to a room of people in our field and then give them time to ask questions and pick apart your research, or poster presentations, which is where you have a large poster with the details of your research on it & you stand around with other people presenting posters while our peers attending the conference walk around and look at the posters, ask us questions, and critique our study. Both oral and poster presentations at conferences look great on CVs (however getting authorship on a publication usually looks best) in part because it is typical for your research to have to pass peer review before getting accepted for presentation. On a CV, national (or international) conferences look best, regional are next best, and state conferences are often weighed least however any acceptance at any conference looks really good and also gives you lots of useful experience.
As far as finding something to work on that relates to your interests.....look at the web pages and CVs of faculty at your school and see if any of them are doing work that interests you. If not, scope out faculty in other departments (sociology, medicine, anthropology, social work, woman and/or gender studies, etc) and see if anyone is doing work that relates to your interests. If so, send them an email and see if you can meet to talk with them about the possibility of you helping them with their research. Also, it may be useful to see if your dept allows undergrads to complete a research thesis. This would give you lots of hands on experience and will allow you to make sure that conducting research (and thereby pursuing a clinical degree) is really what you want to do.
Does this make sense and/or help?