Each service has its own criteria for eligibility, obligated service, application processes and restrictions. This money is usually paid directly to the institution by the individual services.
Additionally active duty members may elect to use the MGIB "top-up" in addition to their service provided TA to cover high cost courses.
TA is not a loan; it should be viewed as money you have earned just like your base pay.
Follow the links for your particular service and start taking advantage of this GOLDEN opportunity: