The writer got mad when a goblin shoved Astarion off a cliff. It reminded me of when I had Karlach shove a goblin in lava, then a goblin ran up and shoved HER in the lava. I didn’t get mad; I took it as a learning moment: enemies can shove me back, so move away from the lava.
I agree, I made some leveling choices not fully understanding cantrips either.
Basically, what they are is a spell that doesn’t use your spell slots. So for example, wylls eltrich blast is a cantrip. You can cast it once per turn and it doesn’t cost any resources, just like a regular melee attack or ranged attack, it just uses your attack move that turn.