How does the role of cell membrane carriers differ from that of channels?

Membrane carriers and channels of both proteins. The carriers simply provide a pathway or tunnel through the cell membrane along which irons or molecules can pass (but many channels are gated, meaning they can be open or closed).
Carriers on the other hand do just what the name suggests-they pick up molecules from one side of the membrane and move them to the other. If the carriers are moving molecules down the concentration gradient and no energy is required they are participating in facilitated diffusion. If they are pumping molecules against their concentration gradient process is active transport.