A timer is a specific type of integrated circuit, which switches signals on and off at periodic time intervals. Although you can build a timer circuit by using transistors, usually integrated circuits are used. They are mass-produced and have a distinct advantage to be integrated simply and reliably in circuits.
Timers are located in a variety of applications, from toys to complex control circuits. Think of a toy police car, flashing its warning lights. But also think of circuits, where a delayed or oscillating signal is needed.
In the further course you get to know the NE555 timer. You build circuits which demonstrate clearly the functioning of the timer. Furthermore you realize complex solutions, such as those used in real applications.
To get started you need to do a few preparations...