Protein channels help in the transportation of substances in and out of the cell.
These protein channels are embedded in the to help facilitate the movement of larger substances that are not capable of just simple in and out of the cell.
Here is a video which illustrates how channel proteins allow particles to pass through the membrane.
The cell membrane is made up of pure lipid molecules that do not permit entry of some substances into the cell. Without protein channels, the cell would starve to death because it cannot receive the organic compounds it needs to function and maintain its order.