Wow, your question is very understandable and I get it that you are thinking this is a dumb question. To most electronic engineers this is a very very bascic Q, BUT our shit education does not teach us these important basics
So dont worry, its good to ask basics if we want to learn!
Digital Signal
Generally speaking digital or analog signal depends where you are giving 5 Volts or 3V or 0V.
If you give 5 Volts to microcontroller then its Digital 1. If 0 volts then 0.
You can rmember like this:
if 5volt then 1 (it is on)
if no volt then 0 (it is off)
But its not exact sometimes, it can be: (0 to 1.2 Volts) as 0. and (4.0 to 5 Volts) as 1 for a microcontroller.
Some microcontrollers can accept 3.3V as 1 and 0Volts as 0. These are all digital signals because you are giving it to a "digital device".
Analog Signal
BUT if you give the same 5 volts to a circuit which has a resistor and a bulb it is considered analog signal. Well, we dont say "Analog signal" usually, just voltage.
Another important thing. Digital circuits is just a collection of many analog devices like capacitors, transistors, resistors and inductors. The same analog stuff we learn in 9th grade. Thats all. Only thing is there are millionns of them in a digital circuit connected together to accept just two signal "modes" ON(5V) or OFF(0V). And diferent digital circuits can accept different voltages a 1 and 0.
Visit this link and keep reaaading
Have fun!
Digital electronics - Wikipedia, the free encyclopedia