There are lots of sections on VMCAS, but most of them are really straightforward. If you're preparing ahead of time, I suggest getting all of your veterinary, animal, and work experience listed out. Your application will go much more quickly if you already have the dates and hours of your experience together. That way, you aren't stuck going "did I work in that research Lab in 2004 or 2005?"
There's only one essay on VMCAS - your personal statement. Two essays if you write an explanation statement. Some supplemental applications have specific questions, but not all.