I have gotten a few PM's so:
Getting a travel card is easy. You can do with the BudapestGo app or if you are like me and don’t want to mess with a phone during the day a paper copy is the way to go.
If you are arriving by plane, then in the arrivals hall, look to your left and you will see the BKK office. I think it has a purple banner above.
If you are coming by train to Keleti Station (most arrivals terminate there) then go to the original arrivals hall constructed in the 1880’s (where platforms 6, 7, 8 and 9 are located) walk to the front and you will see some stairs going down https://www.seat61.com/images/budapest-keleti-steps.jpg Walk down the stairs, and at the bottom on the right is the BKK office where you can purchase a pass https://c8.alamy.com/comp/2AB0K8E/information-and-tickets-ticket-office-of-bkk-budapest-kozlekedesi-kozpont-budapest-public-transport-centre-keleti-palyaudvar-budapest-hungary-2AB0K8E.jpg
There are also machines outside where you can purchase the passes, but it’s a lot easier to get the help in the service center.
Buying a card in town. If for some reason you don’t want to purchase the TravelCard at Keleti or the Airport, again there are machines at most metro locations and some of the tram stops, or there is a BKK service center in the Deak Fernec ter metro station.
Deak Ferenc ter is sort of Ground Zero for all of the sites of Budapest so you will be near it a lot during your stay.
It’s a big underground so to make finding the service center easier, set your google maps for Deák Ferenc tér 6, Budapest, 1061 Hungary. No way you can miss it: https://c8.alamy.com/comp/2M5P8D1/budapest-hungary-front-view-of-beautiful-old-building-of-anker-palace-in-the-city-center-2M5P8D1.jpg
At that location you will see stairs down and the service center is on the right at the bottom of the stairs. The MILLENNIUM UNDERGROUND MUSEUM is located in the back of the service center and is sort of interesting.