寄る and 寄せる: stopping by and moving closer
Compare a place stopped at along the way with an object moved closer, distinguishing a stopover from the final destination.
Stop somewhere on the way
帰る前に、スーパーに寄ります。 says that the speaker will stop at a supermarket before heading home. With 寄る, read よる, に marks the stop.
友達の家に寄ってから、駅へ行きました。 says that someone stopped at a friend's house before going to the station. The house is an intermediate stop, with the station as the subsequent destination.
Move closer to something
写真を撮るので、もう少しこちらに寄ってください。 asks someone to come a little closer for a photo. 寄る here does not mean making a brief visit.
椅子を机に寄せました。 says that someone moved a chair closer to the desk. 寄せる, read よせる, uses を for the chair and に for what it approaches.
Gather things to one side
荷物を部屋の隅に寄せてください。 asks someone to move the luggage together toward a corner of the room. It does not ask them to discard it or take it outside.
寄って is the te-form of 寄る and 寄せて of 寄せる. Learn 人が寄る and 椅子を寄せる with their subjects and objects to identify who or what moves.
What is moved in 椅子を机に寄せる?
Show the answer and why
The chair. 椅子を is the object moved, and 机に is what it is moved closer to.