You can go into the service after you complete high school. You can select a branch of service based on your interests and upon the training that they can offer you. You might decide to remain in the service as a career, or you might want to get out and continue your education with the military paying for your education.
Start by talking to your school counselor and taking interest and aptitude testing. This will provide an idea for you to use as a military career if you decide to go into the service, or as a career to continue your education for, if you decide not to go into the service. You can get a good career and good education either way, as long it fits with you.
Remember to send thank you notes to all who help you.
I will be happy to help further if I can.