Many students who go on to Law school got a start with volunteer groups in their undergrad. Once you become a lawyer, you are restricted to practicing in the jurisdictions where you pass the Bar examination, unlike with volunteer groups where you can travel and work in different communities. A Raleigh, NC divorce lawyer is not going to be able to practice family law outside of North Carolina without getting certified to practice law in those areas first.
On a similar note, if you want to practice different types of law, it is common for lawyers to specialize in different fields. If you work in Florida as a Jacksonville Injury Attorney, it wouldn't be unusual to also work with other personal injury clients. Make sure to explore plenty of options in your law education to see what subjects you might be interested in.