Follow the wiring diagram you posted. That is all you need
https://i.ibb.co/7zVvMQ2/20240403-194808.jpg
Follow the wires in down from top left
The hookup from wires left to right and from terminals top to bottom are R, C, G, W1, W2
Red is 24V
C is transformer common
G is green to activate fan
W1 is heat stage 1
W2 is heat stage 2
If you have AC there should be a yellow fed through from the outdoor condensing unit, coming through into the furnace and fed up to the stat to fire up the outdoor unit
I would NOT assume that wire colors follow up to the stat, check them out continuity, etc
EG example: We added AC to the neighbor's son's house, and someone evidently, when building the house, caught the stat wire on a duct joint and yanked it, stripping and shorting 2 of the stat wires to the duct and furnace ground. I've forgotten what colors, but this was a 6 wire stat and we only needed 4, so the stat is wired with incorrect colors to get it to work. The stat wire is unaccessable in parts of the house