"I could eat this fish sandwich."
Translation:Ich könnte dieses Fischsandwich essen.
Konnte is the normal past tense. Könnte is more like a possibility or philosophical statement. It's kinda like the difference between "when I was a teacher..." and "if I were a teacher..." One is past tense, the other is more a philosophical statement (which is named the subjunctive). It's hard to explain without using the "greek". Sorry, I hope you get it though!