Yes it's possible, depending on what your department need, ask your supervisor and they may be able to point you in the right direction. I started teaching in my third year and now (in my fourth) I have a full time lectureship. Teaching is a worthwhile experience and it can help with finding a job in academia (in conjunction with publications etc), but as other people have said it can take up a lot of time so be careful not to take on too much as it could really slow down the PhD research.