What does the receptor accomplish for the cell?

The receptor binds to several ligands, undergoes a conformational change, causes a signal cascade by stimulating other protein molecules and enzymes like Protein kinases and results in response to a particular chemical(ligand).

A receptor is a protein embedded in the membrane or the cytoplasm of the cell. It will bind a mobile molecule which is termed a ligand. A ligand can be a peptide (such as a neurotransmitter), a hormone, a pharmaceutical drug, or a toxin.

Some receptor binding of the ligand will cause a confirmational change in the receptor, inducing a cellular function/biological function. This is done by inducing a singaling cascade which starts with the ligand binding and the confirmational change in the receptor. Example - Glucagon receptors and chemokine receptors.

But sometimes ligand binding can block the receptor and this blocks the responses. Example - antagonists