Complex sentence: Cell surface receptors (membrane receptors, transmembrane receptors) are receptors at the surface of a cell (built into its cell membrane) that act in cell signaling by receiving (binding to) extracellular molecules.
Split into simpler sentences: Cell surface receptors (membrane receptors, transmembrane receptors) are receptors that are built into the membranes of cells. They act in cell signaling by receiving (binding to) extracellular molecules.