Before you start, make sure you have a copy of the college courses you intend to take in the coming semester. Tuition Assistance must be filled out before the first two weeks of the semester (or before the final add/drop day at your university). Once you've gathered this material, make sure you have access to the internet.
Log in to your AKO account. The military has done a good job of automating the TA (tuition assistance) application process. Go to the My Education tab.
The form you need to fill out is DA 2171-E. If you can't get it to fill out correctly online, you can print the form and fill it in by hand. On the form, note the courses you will be taking, how many credits they are, and how much the school charges for them. Usually there are instructions that accompany the form. Make sure to complete all of the information pertaining to your courses.
Once you have signed the document and entered your phone number, you need to submit it to your supervisor at your unit. They will get this form to the commander for their signature. Once the form is returned to you, submit to your unit's education office. After they process the form, they will disburse the funds to whatever account you use for your military paycheck.
Remember, you must contact your education office at the end of the semester and report your grades. Tuition Assistance can only be used for classes in which you get at least a B. If you don't report your grades, or get less than a B, the military may decide to recoup the money they paid you.
The great thing about Tuition Assistance is that it doesn't affect any of your other military education benefits. You can draw Tuition Assistance and the Montgomery GI Bill for the same courses, so don't hesitate to take advantage of this program.