I hate to break it to you, but if you can't pass MEPS, you won't get on the board. MEPS is the Military Entrance Processing Station. All branches use the same MEPS, just at different locations. Your MEPS results are usually good for two years, so your OSO may have you go to MEPS early in this process.
MEPS is an in-depth medical screening. They will test you for vision, hearing, range of motion, skin, othopedics, etc. You will need to bring your medical records. In the past, recruits would lie. Nowadays, medical records are electronic and a new system called MHS Genesis can pull a lot of records. You'll not be able to contract if you lie at MEPS.
If you ever had a health problem in the past, you won't pass MEPS the first day. You will get temporarily rejected until your medical paperwork saying that the illness is gone or the injury is gone is approved by a higher medical authority. This is called a "waiver." Waivers are given out for many things, including surgeries and minor conditions.
Things people commonly fail at MEPS:
The duck walk (it's a squatting walk. Don't sweat it)
Drugs (it does happen)
Hearing (a lot of people find out they have hearing loss at MEPS)
Severe allergies
Scoliosis
Mental Health
If you are older than 28, you can get an age waiver like I did.
Another part of MEPS is the legal aspect. I'll explain more about this on the next page.
At MEPS, a lot of people take the ASVAB. I'll explain more about this on the Academics page.