Switches are used to start and stop the flow of electrical current.
A push switch only lets current flow when a button is pushed. Where a push switch is in the circuit, the wire line is broken, with two empty circles drawn at either end of the line. Beside these circles, but not touching them, is a straight line. The symbol suggests that if the straight line were pushed, it would touch the two circles, forming a connection in the broken wire.
A push-to-break switch stops the current flow when it’s pushed. Its symbol is the same as that of the push switch, except the line segment is touching the empty circles (as if waiting to be pushed away so that it breaks the circuit.
An on-off switch starts the current flow when it is closed. It is indicated by a gap in the wire with empty circles at either end of the break. Attached to one of the circles is a straight line that is positioned at a diagonal to the wire line, such that it doesn’t connect the two circles.
A two-way switch is like an on-off switch, except it can send the current in one of two directions, meaning one of the two is always on. Its symbol looks like the on-off switch, but the diagonal line segment touches two of the three wire ends at the gap in the wire.
A dual on-off switch is like the on-off switch, but with two such switches parallel to each other. When the switch is hit, both turn on or turn off. It is indicated by two on-off switches drawn parallel to each other.
A reversing switch is like a two-way switch, but with two such switches parallel to each other. It is indicated by a pair of two-way switches drawn parallel to each other.
A relay is a switch that is electrically operated. It is indicated by three wire endings: one labeled “normally open,” one labeled “normally closed,” and one labeled “common.”