What Are The Differences Between Isometric And Isotonic Contraction?

Isotonic - I read that in your arm for example the biceps contracts it shortens this lets you lift your forearm & whatever your carrying,
Isometric - If you are carrying something heavy like a suitcase it makes you unable to lift your forearm, the biceps do not shorten as much as if your lifting your forearm but the force the muscle generates helping to carry the suitcase