In a 4/4 time signature, 1 bar (or measure) equals 4 quarter notes. That's the count-in (1, 2, 3, 4) -- quarter notes.

Eighth notes count like this: 1 and 2 and 3 and 4 and -- they divide the measure into 8 subdivisions.

Triplets would divide the quarter note into 3 --- so:
1 (2 3) 2 (2 3) 3 (2 3) 4 (2 3) --- 12 subdivisions

Sixteenth notes count like: 1 e and a 2 e and a 3 e and a 4 e and a --- 16 subdivisions in the bar.

And so on and so on...

Make sense?
Mike