People often think of contraception in terms of condoms and "the pill". There's actually a pretty wide range of options out there for those that want to avoid unplanned pregnancy.
Condoms are talked about most often, because condoms protect from both pregnancy and STIs. If you're using a form of contraception that's not a condom whilst having sex, then you should use a condom to prevent STI transmission unless you're sure the other person doesn't have an STI. You can get most forms of contraception at GPs, GUM clinics, and some pharmacies; for more information, see the "Where can I go to get a sexual health check-up?" question below.
The range goes beyond condoms though. There are pills, female condoms, caps, injections, implants, patches and more. For more info, see the NHS's explanation of the options.