Lots of great tips above.
In general you want to to have a slight bend in your knee when your pedal is at the bottom of your stroke.
Google will show you lots of videos/tips on getting the saddle height right.
Too low will have have pretty much all your weight on your bum and will hurt your knees too.
When the saddle height is set right then your weight will be more evenly distributed between your bum and your arms and legs.
As others have said, standing up regularly to give your bum a rest will help too.
You don't even need to pedal while you stand up if you don't have the strength or confidence.
As long as you are on the flat or downhill you can simply coast for a little bit to give your bum a rest.
In general you want to to have a slight bend in your knee when your pedal is at the bottom of your stroke.
Google will show you lots of videos/tips on getting the saddle height right.
Too low will have have pretty much all your weight on your bum and will hurt your knees too.
When the saddle height is set right then your weight will be more evenly distributed between your bum and your arms and legs.
As others have said, standing up regularly to give your bum a rest will help too.
You don't even need to pedal while you stand up if you don't have the strength or confidence.
As long as you are on the flat or downhill you can simply coast for a little bit to give your bum a rest.