Plain English is perfect — write it the way you'd explain it to a new member of staff.
e.g. two-vet small-animal practice with 3 consulting rooms
Session lengths, rooms and practitioners, how patients book, reminders
Check-ups, vaccinations, hygiene appointments — cycles and how you chase them
Consultation fees, treatment plans, insurance claims
Clinical notes, consent forms, lab results — and what would need migrating
The workarounds, the spreadsheet on the side — that's the part we tailor around
Monthly fees, per-use charges, commission — whatever you pay