I LOVE YOUR POSTSince you can light an LED, the next step would be to use a transistor as a switch to the LED on and off with a an applied voltage. In doing so, pay attention to which side of the transistor the LED and resistor are connected to, and why. Beginners usually get that wrong. Also make sure that you understand why the base of the transistor cannot be connected directly to a voltage source.
Once you understand that, see how you can add a capacitor to make the LED fade on or off. That will introduce you to the linear region of transistor operation.
Then a multivibrator will be within reach pf your understanding. It can flash two LEDs alternately.
Next, learn how you can use a transistor to amplify an audio signal.
You can learn about Zener diodes by making a simple voltage regulator.
Then learn how you can add a transistor to your simple regulator to give it the capability for higher current and better regulation.
This should keep you busy for a while!
Bob
Bob