When taken perfectly (i.e. at the same time every day), it is 99% effective, which means that of 100 pill users who are sexually active for a year, 1 will get pregnant.
If that sounds like too high of a risk for you, you can still use condoms if you want. It might also be a good idea to use condoms if you know you don’t take your pill perfectly as directed.
If you do, though, it’s not necessary to use condoms (that’s the point of being on the pill) unless you want to be really really safe.