Why the på?
In English, you could also say "He spends his weekdays on swimming."
But why do we need both "på + at" ?
I though I was starting to understand these things and now I see them combined in a sentence, I want to cry
And why is "på" not also indicate, when I tap the verb?
I believe the reason for the på is to go with bruger, because generally when you spend something, you spend it on something. So I think it should be thought of as "bruger sine hverdage på" as one part, and the "at svømme" separate.
*Literally 'on to swim' - på at svømme
*at svømme - swimming
*svømme - swim
So many words with the same meaning im confused
Hang in there. Sometimes some language features don't make sense to a non-native speaker and just need to be memorized. You will get it eventually.