Describe symbols on a schematic? What is a printed circuit board?

A schematic is a drawing that represents an electronic circuit using standardized graphic symbols rather than physical appearance. Each component type has a conventional symbol so that any engineer can read the design: a resistor (zig-zag or rectangle), capacitor (two parallel lines, with a curved/filled plate for polarized types), inductor (coil), diode (triangle pointing into a bar, with variants for LEDs and Zeners), transistors (BJT and MOSFET symbols showing base/gate, collector/drain, emitter/source), integrated circuits (boxes with labeled pins), connectors, switches, and power/ground symbols. Each symbol carries a reference designator (R1, C3, U2, etc.) and a value or part number, and lines between symbols (nets) represent electrical connections, with dots marking junctions. The schematic captures the logical/electrical intent of the circuit independent of physical layout.

A printed circuit board (PCB) is the physical substrate that mechanically supports and electrically connects components. It is built from an insulating laminate—most commonly FR-4, a glass-reinforced epoxy—clad with copper foil that is etched to leave conductive traces, pads (where component leads/pins are soldered), and copper planes. Vias are plated holes that connect traces between layers on multilayer boards. A solder mask (the typically green coating) insulates and protects the copper while exposing pads, and a silkscreen prints labels and outlines. Through-hole and surface-mount components are then mounted and soldered to realize the circuit drawn in the schematic.