As far as you are concerned Boeing = Airbus = a big one
Learjet = Gulfstream = medium sized
Citabria = Piper = Cessna = small one (usually), if you want to get clever you could also try to remember that Cessnas tend to have their wings on the top.
The complicated bit may come when ATC tells you to "park behind the cessna", if you don't understand then just ask ATC to elaborate and they will say it another way, eg "yellow high wing" .... you will look ignorant ..... but maybe that does not matter.
My wife was once told to park "behind the Lightnings" (this was some time ago) and when she queried was advised to look for the "pointy ones" (cue sexist comments in the tower).
I will say that, in aviation, trying to scrape by with the minimum knowledge does not really cut it. Sooner or later you will be alone in an aircraft without anyone to ask.