Some machines, like Easy-Bake Ovens, don't need any help when doing something. Active sonar's just like that: it's your one-stop shop for wave creation and detection. Some versions thought about adding in the functionality of the Easy-Bake Oven, but they decided that was a little tangential to the main point of the sonar.

Even if it would be delicious.

In an active sonar system, the sonar itself both creates and detects waves to figure out where things are. In order for that to happen, the electrical energy from the transmitter (the part that transmits the wave) needs to be converted into acoustic energy. In general, the part of the sonar that turns electricity into sound is called the transducer, which can both send and receive the sound signal while it converts between sound and electricity.

(In case you were wondering, a transducer that can only receive sound is called a hydrophone, and one that can only transmit is called a projector. Sonar usually has a transducer that does both, though.)

Active sonar creates a pulse of sound and then listens for reflections of that pulse after it hits something and bounces back. That pulse might be a single frequency, but it could also be a series of changing frequencies. If it's a series of frequencies, the signal's called a chirp signal. That way, when a chirp comes back, the receiver can test it against every possible frequency to figure out if the return signal is associated with a sent out pulse.

Once it can match the associated frequencies, then we can figure out the time difference between when the sound was sent and when it came back, which is a short hop away from being able to tell what kind of distance the sound traveled before bouncing back towards us.

Things get a little more complicated when sound waves start mixing together with the ambient noise in the water, but that's a story for another day.