Select two opposing edges and press F to fill to create one face. Then as long as you have quad topology (four vertices per face) you can select the vertical edge on the face and just hold F and it will keep adding faces until you’re around or you hit an n-gon.
Or you activate the built-in addon Mesh: Loop tools. With that activated you can select both edge loops -> right click -> loop tools -> bridge. This will connect both edge loops with clean topology.
