Catheters are not something to play around with lightly. Please make sure you thuroughly clean all work surfaces, and your hands, and genetalia, before attempting to insert one.
Only use folley type baloon catheters for semi-long term use (you will need a syringe and distilled water to inflate the baloon), as straight intermittent catheters will migrate out of your body when not actively held in place. You will need plenty of good numbing lube too. I found one good type is called anal ease. It works to numb pretty good, is intended for use in the body, and is available over the counter.
Stay very well hydrated with one in too and consider drinking lots of cranberry juice (or take cranberry pills) to help lessen the chance of getting a UTI.
Even with all these precautions, inserting/removing the catheter will likely hurt. Possibly producing a little blood too (this is normal). That pain should go down to tolerable levels within an hour or two. If it doesnt, go to the ER.
Once it does though, you can safely let the catheter drip drain into your diaper. You will likely not notice getting very wet, so make sure to check and change your diaper periodically. Periodically reapply the lube at the tip of your penis too. If the catheter dries out, those size changes we get can catch it and get pinched in a bad way.
Lastly, it's better to not mastrubate with a catheter in place, though you can without lasting damage to anything. Just make sure the catheter is very well lubed, and expect it to still hurt a little.