Are you still Active Duty? Your profile says CTI2, so I'm assuming so. Anyway, go to the Correspondence Course website listed below and look at the Basic Machines course. This provides a comprehensive overview of mechanics in laymans terms. There are also many good resources for study guides listed elsewhere on this forum. There's apparently a very good study guide that you can download. I'm sure someone who knows will point you toward it. I'm an ET hoping to cross over to your world (Crypto Officer), just waiting for a response.
https://www.advancement.cnet.navy.mil
Good Luck!