freebeer
Thanks for the update.
You *really* (imho) want to use a full workstation / desktop machine with full mouse to do any serious editing, if my experience with a beginner-level tablet is anything to go by.  But then, I never saw the attraction of many things in common use nowadays.
You may be able to get an attached mouse to function, but in my experience I was unable to use the scroll wheel or additional buttons for the functions I expect.
There are reasons I view such tablets and smartphones as toys, and they see little use from me.  could also be the limitations of the model I inherited.
When you ask for all buildings, then even I as a still-beginner cringe, probably because I have not graduated from my editor Potlatch 2 to JOSM.
Perhaps other mappers are using android to get the results I admire, in which case I shall withdraw my reservations.
If you have access to a desktop or even a notebook OS, see if you get further, else I shall defer to the more experienced.
FYI, I am on an awful network connection so it takes some time, perhaps a minute, for my Potlatch to be ready, for each editing session.  The recommended starter editor, iD, seemed to take even longer (more minutes) before being fully populated.  Almost nobody else should see such a problem, and it's one of many more important and pressing problems on my FIXME infrastructure list.
Hope that helps.  Imagine you're going to do some fingerpainting, or have a set of fine brushes and pointy pens to hand.
good luck!