What are the differences between geometric isomers and optical isomers?
And see here for here a discussion on diastereoisomerism.
Just to review the levels of isomers, structural isomers are species with the same chemical formula but different connectivity. Geometric isomers have the SAME connectivity but different geometry. The best illustration of geometric isomerism occurs with cis and trans
Chirality, handedness, adds another level to isomerism. Enantiomers have EXACTLY the same connectivity, and geometry, however, one enantiomer is the mirror image of the other. Introduce a couple of so-called chiral centres into the molecule, and diastereomers can be generated, i.e.
If there is something I have ignored fire away.