As an introduction to learning about rhythm it is important to realise that, in practice, this is the most difficult concept to grasp of all the logic behind performing music.
The organisation of notes into bars and the detail involved in this presentation requires some time and study to be efficiently aware of the set-up.

A simple framework within which to work:

Using this as an example, we can read the rhythm as:

Slow, slow, very slow, Slow, slow, very slow,

Using this as an example, we can read the rhythm as:
Bar 1: Quick, quick, very quick very quick, very slow
Bar 2: Very slow, very quick (quick being the rest!), quick, slow
Bar 3: this is a rest, hanging from the line, and lasts for the whole bar.