How do i get my muscles to show up more?

If you want to have the look of a more defined muscle then you should lift heavier weight and less reps. If you want to tone then you use lower wts and more reps. As far as bulking up it takes quite a long time to get really bulky. At your age 13 you are still growing so I think in a couple years you will bulk up naturally. Just give it time. swimming and and any activity or sport is good. It is more important to eat a balanced diet so your body can have the proper nutrition to develop muscle later on. Eat lots of protein complex carbs and fresh fruits and vegtables. good luck.