Layout vs Schematic in Altium Designer
Design Rules Check (DRC) will check the connections on the PCB against the netlist generated from the schematic, and report any differences (missing or extra connections).  It will also check trace widths, clearances, hole sizes, and other PCB-specific details against the PCB design rules, and report any violations.

You should also run Electrical Rules Check (ERC) on the schematic.  This will report unconnected input pins, multiple outputs driving a signal, and other errors that may occur on the schematic.