Circuits normally start life as a circuit diagram drawn on software such as Crocodile Technology. Opposite is an example of a light sensor circuit drawn in this way. Crocodile Technology can simulate circuits working.
When the light level is low the resistance of the LDR is high. This prevents current from flowing to the base of the transistor. Consequently the motor does not rotate.
However, when light shines onto the LDR its resistance falls and current flows into the base of the transistor and the motor rotates.

A circuit design can be exported from Crocodile Technology to Real PCB, which converts it to a PCB layout, ready for manufacture.
This is a view of a light sensor circuit with its components soldered to the manufactured PCB. The copper tracks are on the underneath side of the PCB. The components are arranged on the top side of the board.
Sometimes software such as Real PCB cannot connect all the components with tracks as it would mean that they would cross each other. ‘Fly wires’ (the brown wires) join components that cannot be connected by the copper tracks.

When the PCB is ‘flipped’ over the copper tracks can be seen. The legs / pins of components are soldered on this side.

QUESTIONS:
1. Draw a circuit using software such as Crocodile Technology. Run a simulation of the circuit to see if it works.
2. Export the circuit to software such Real PCB, convert it to a PCB layout and manufacture the Printed Circuit Board.