Gonorrhea (or the clap) is a bacterial infection which often causes pain when people with a penis urinate (although not everyone experiences this symptom). For people without a penis, roughly half of those with gonorrhea do not experience any symptoms at all. Some people experience a white discharge from their genitals from gonorrhea, but again, many may not. For people with a uterus, if left untreated, there is a lot of evidence that it can cause serious complications with menstruation, or pregnancy.
Gonorrhea can normally be easily treated with antibiotics, although some strains of it can be tougher to get rid of.
If you experience pain while you urinate, or an unusual discharge from your genitals, you should see your doctor or a sexual health clinic. They'll normally do a simple urine test, although some cases might need other testing.