[tiedieconderoga]

"Digital electronics" communicate using discrete values, 1s and 0s.

"Analog electronics" communicate using voltage/current/temperature/etc levels.

One of the simplest examples is a voltage divider: if you put two resistors across a DC voltage source, like this:

    V+-[R1]-¢-[R2]-GND

The voltage at the ¢ point will be:

    V+ * (R2 / (R1 + R2))

There are infinite possible values for that voltage, depending on the voltage source and the two resistors. It cannot necessarily be expressed exactly in a digital circuit, and it will fluctuate over time as the environment changes in temperature, humidity, EM noise, and so on.

I usually recommend The Art of Electronics as a well-written, beginner-friendly textbook which covers the basic concepts.