Well as their name implies granular leucocytes have granules, while agranular do not. Granules are composed mainly of lysosomes from what i remember, and depending on the type of cell, have different affinities for laboratory dyes. for example eosinophiles have granules that turn blue when stained with eosine.
For the characteristis, have a look at any physiology/immunology book. It’s too much info to write here.