Entering a submission grappling or BJJ competition usually costs an entry fee. Anywhere from $25-200 usually. As far as MMA, you oughta be getting paid for that or it should be free. The gym you train at will normally set up your fights for you.
Check out the grappling and striking sections, they've got plenty of tips and techniques that will help you along your way.
Enjoy the Forum and stay active. Feel free to ask any of the Staff questions, as we are here for you.