This was my experience.
I arrived for my appointment & checked in at the front desk. I was taken to a very small waiting room full of very old people. One woman sitting directly across from me gave me a very disapproving look which left me asking myself the question "is it my tattoos or is that just her face?" I waited about 5 minutes before someone came to get me & took me back to what was basically a TINY dressing room. There was a mirror, some magazines, a small basket with alcohol wipes to remove my deodorant (do not use any deodorants or performs the day of - I forgot). She told me to take off everything from the waist up (so don't wear a dress or one of those jumpers like when we were little, the ones that make peeing really difficult) & put on the hospital gown on with the opening in the front - easy access to your boobies. She said someone would be back for me soon. I waited another 5 minutes while taking selfies & playing Sudoku on my phone (maybe it was 10 minutes). Eventually another woman came back to get me. I had hoped it would be like a nice little old grandma who would talk gently to me & make me less nervous. She wasn't. She told me to leave my clothes but bring my bag with me. She took me into a large room that looked like every other doctor's office but had a giant machine in the middle. It also had two TVS playing what I assume is supposed to be relaxing scenes to help distract you during your mammogram but except she had me take my glasses off so I couldn't see anything while I was getting it done.
The first thing we did when we got into the office was she had me sit down & then she asked me basic questions like my name and age. She then asked if there is a history of breast cancer in my family, she asked if my grandparents were alive (one set is, one set isn't - she needed to know which), she asked if I had sisters & what their names were & if they were "alive & well" (they are!) She then went on to ask if I had any breast surgeries (the paperwork I did before my appointment had asked about implants so I imagine the process may be different for people with implants?) She asked if my mom had sisters & what their names were. There were a lot of questions.
Then it was time!
She allowed me to only expose the breast she was x-raying with my arm in the gown and had me stand in front of the machine facing forward, sorta hugging it. She then adjusted my position and placed one breast on the plate which she had put a foam like cover on (I don't know what that is for - comfort maybe?) She was not gentle with moving me around. It actually felt very aggressive which would be my only complaint. Like, she PUSHED me a couple times. She "marked a mole" I didn't even know I had that was towards the back of my armpit. She put what was sort of like those round white stickers you use on paper in your binder if they rip - ya know what I'm talking about? After she had me situated my body with my breast on the plate and my arms hugging the machine she brought the second plate down. Now, this is where I'm sure opinions will vary. I did not think it hurt, I didn't think it was uncomfortable. I didn't think it was much of anything because it was like that for MAYBE 2 seconds. I barely had time to react (but I also have a high tolerance for pain). The machine lifts up on it's own after the picture is taken (I'm sure she's controlling it but she doesn't actually touch it) She said "perfect" or something along those lines and then said "let's do the other one now". Rinse. Repeat. Then we moved onto side views which she had me take my arm out of the gown for but still allowed me to keep my other breast covered. The machine turns so you can just stay in the position you're in, with slight adjustments. Then we did it again, twice. Again it took barely any time at all & the only uncomfortable part was her pushing me around which I almost think might be intentional, almost like a distraction so the smooshed boob part isn't as traumatic? This part took maybe 5 minutes total, but probably less.
She declared we were finished & said she would walk me back to the room where my clothes were. She told me to get dressed, showed me where there was deodorant wipes if I wanted to use them. She said she would walk me out after I was finished getting dressed. When I was finished she handed me an appointment card for next year's appointment, explained the results would be sent to my doctor and made available to me on the app the hospital uses and then she showed me the door and my first mammogram was successfully complete. My doctor did explain that often the first mammogram may come back with some suspicious looking things, but not to be alarmed. Younger people have more dense breast tissue which can make it difficult to get a clear image and with your first mammogram there is nothing to compare it to. She told me not to panic if I am asked to come in a second time! Also, I have health insurance through my employer but if you do not have health insurance there are lots of ways to still get your yearly mammogram. I googled "mammograms without insurance" & got a lot of results - so many so, that if it overwhelms you email me at firstname.lastname@example.org & I can help you find one! Thanks for reading & good luck with your first mammogram!