I don't know much about the guard. I think if you spend some time on this website it will answer a lot of your basic questions, and help you to come up with more questions! Then, you should talk to a recruiter. https://state.nationalguard.com/texas?cid=amrgfloodlighttagsanddisplayads_66_amrgads_web
Best of luck!
You can also dial 1-800-GO-GUARD to ask questions about becoming an MP (Military Police) which is MOS (military occupational specialty) 31B.
This address has further information: