Make sure you don't have any serious medical conditions that aren't addressed. Blood pressure is a big one. However, given that spironolactone is a blood pressure medicine (Potassium sparing diuretic) they can probably start you off with that right away even if you don't get estrogen.
If you have seen doctors for other stuff before, get them to transfer your medical history, or download it from the patient portal (if your doctor has one) if you can and bring it with you. Blood work showing things like liver levels, HgbA1c (diabetes test) are helpful. Otherwise they will probably do a lab test and you'll get your hormones on a follow up visit.
They'll likely start you off on a small dose and you'll get the full dose in a few weeks. The idea is not to shock the system with a hormonal u-turn (as Ms Grace put it so aptly). You may get the choice between injections and pills, but you might get started on pills initially.
Otherwise not much different from a routine doctor visit. I have heard of things like checking the size of the testes and breast exams but she did none of that with me. All she did was take my blood pressure, do some tests on my feet for diabetes (to see if I lost feeling) and talked with me about HRT and medication choices for blood pressure.
