The foreskin is too long: the foreskin covers the urethral orifice, but it can be turned up to expose the urethral orifice and the penis head. After erection, the glans penis can be exposed. If the foreskin is too long, just open it and clean it every day.
Phimosis: The narrow mouth of the foreskin or the adhesion between the foreskin and the penis head make the foreskin unable to turn up, exposing the urethral orifice and the penis head. You can't expose the glans after erection, and you can't expose the glans with your hands. Phycosis needs prepuce surgery, otherwise it will lead to glans necrosis due to prepuce incarceration.