Many faculties will seek to hire undergraduate students for tutoring opportunities (although not every faculty will). Tutors are valued for their
ability to teach (not necessarily the marks, although good marks help) and willingness to actually spend time focusing on students' needs.
In some (arguably many) scenarios you will start with an easier role than actual tutoring. This could involve being a revision class holder, or just a lab assistant. Your responsibilities, whilst serious, are a bit more relaxed because you do not have the added pressure of things like marking, supervising and preparing for lessons alone.
Tutorial sizes generally range from 18 to 40 (although in some cases there are small tutorials of 5; been in one myself, and huge ones of up to 60). The way tutorials are run differ for each faculty, however you should be familiar with how they work (roughly), because you've sat through a bunch of them