If the time is 4/4, the following notes would be: A quarter note (1/4 or 2/8) of the measure) A half note (2/4 or 4/8) of the measure 2 eighth notes (2/8) of the measure.
It extends the note for half it's value for example: a dotted quarter is worth one and an half beats.A dotted half note is worth three beats.a dotted whole note (which is rare) is worth six beats....