PrEP is a pill you take before sex without a condom. You can take it every day or only when you need it.
PEP is a treatment you take for 28 days after possible exposure to HIV. It must be started within 72 hours of sex without a condom with someone whose HIV status is not known. PEP works best the sooner you start it.
If you think you need PEP, go to a sexual health clinic or A&E as soon as possible. A doctor or nurse will talk to you and decide if you need it. It helps if you can share any information you have about your partner.