SKY-DECKS SETTINGS

Hey guys I need some help, recently I purchased Sky-Decks panel design
Boeing 737-ng ...ok the model is a joy to fly however I need some clarification on how to use the N1 feature.
Exactly when are you suppose to turn it off, and are you suppose to have the CMD-A button engaged? I have noticed if the CMD-A button(autopilot) is engaged the aircraft rotates by itself!! Dont think thats right. Also what does the “DELTA” symbol in the SPD REF dial refers to? I’m assuming the Vref is the takeoff V2 speed, but i dont know what the DELTA synbol is refering to. I can hear the audio on the rollout telling me delta is ready....but have no idea what it means. I would guess maybe all systems are set?