Every tyre has its safe pressure range printed right on the sidewall, usually as a min–max in PSI or bar. That range exists for a reason: too low and the tyre pinches on potholes and wears unevenly, too high and it loses grip and rides uncomfortably harsh.
Within that range, heavier riders and rougher terrain generally want the higher end; lighter riders and smooth paved commuting can sit toward the lower end for a more comfortable ride. Mountain bike tyres typically run lower (20-35 PSI) than narrow road tyres (60-100 PSI) simply because of tyre width — more air volume needs less pressure to support the same load.
Check pressure by hand or with a gauge before longer rides — tyres lose a small amount of air naturally over days, and a soft tyre is one of the most common causes of a mid-ride flat.