How do I fix the engine of my car?

This would depend on how complex the repair job is. But essentially you will need 
1. A basic set of tools including spanners, screwdrivers and pliers.
2. An automotive manual for the model of your car. For example a Haynes manual.
3. Once you have diagnosed the problem, watch some videos on YouTube on how to fix the problem.
4. Based on the knowledge that you have gathered, attempt to fix your car

If you are enable to fix it, go to an experienced mechanic.