I did several things. I did work for community members who paid the organization (i.e. raking leaves, shoveling snow) by myself. I went on builds (just typical building a house). I helped with fundraisers for the colleges organization, and I went on a spring break trip and spend the week building a house there. I also assisted with setting up a sale of unused products.
It sometimes can involve heavy lifting (like boards, maybe bricks). You will usually do typical things like painting, hammering nails, drywalling, etc.. If you don't know how to do something, the organization keeps people who know how to do things on-site that will help you and teach you.
I enjoyed it somewhat. It was difficult getting to the 8 am builds on saturday morning while living in a dorm that partied until at least 2 am. The spring break trip was a lot of fun even though I spent a long time standing on ladders.
Whether you enjoy it really depends on your personality I think. I'm okay with physical stuff, but some people really enjoy it. It is worth a try though, and if you don't like it, it is only a few hours of your time that you lost. Just be careful and follow all the safety procedures.
For every house that habitat builds in the US, they build one overseas. Some people I know went abroad to build houses, and they had an amazing time.