Either usually works (or is that works usually? :lol
- I like to help people (infiinitive)
- I like helping people (gerund)
There may be a tiny difference but hardly worth noting. It may be that the first one may put the empasis on "people" (It's people you like to help) whereas the second may suggest you are just a helpful person (It's the helping you like). But that is so hard to distinguish in writing, it's perhaps not worth the concern.