After appendix surgery, doing intance activities could you develope having hernia? How can you tell if you have hernia or not?

If hurts, don't do it. Wait at least 2 weeks after a lap appy before you do any heavy lifting. We usually rec'd no lifting > 20lbs for 2 weeks. A hernia will present with a bulge that gets bigger with abdominal pressure. A seroma will stay the same size.
Doing too much. If you lift heavy things, cough a lot, do too much exercise before you're healed, it can cause a hernia. It would be a bulge at an incision which changes size, ie gets bigger with effort then smaller when you relax.
Unlikely. Hernias in appendectomy incisions are very rare. The muscles of the abdominal wall overlap in different directions in the right lower quadrant so the open approach rarely causes hernias. Hernias are also unlikely from the port sites after a laparoscopic appendectomy. Obesity increases the risk in both cases and makes detection harder. If in doubt, follow-up with your surgeon.