There are sections for personal info, academic history, work/experiences, research experiences and pubs/abstracts/presentations, awards, hobbies and interests. You also have to submit a photo, upload your personal statement, release your USMLE transcript (there is some nuance to the timing of this in relation to Step 2), and have your letters uploaded.
Then you have to choose the programs to apply to and pay a bunch of money.
I don't remember there being a practical limit on the number of things you can list.