Doctor Thomas Nuhse explains that proteins are the molecules in cells that perform the key functions of the cell. They are the building bricks of the cell.
Proteins are a large group of molecules, one group of the molecules of life if you will. Proteins are essentially those actors in cells that do stuff - they can degrade molecules, they can build the building bricks that our cells are made of. Some proteins also have structural functions, so the shape that our cells have is also determined by proteins in a large part. So, essentially anything that happens in the cell is brought about by proteins.