pronouns
nominative dative accusative prepositional
yo me me
te te
él le le (him), lo (it) él
ella le la ella
ello -- (lo) (ello)
nosotros nos nos nosotros
nosotras nos nos nosotras
vosotros os os vosotros
vosotras os os vosotras
ellos les los ellos
ellas les las ellas

Prepositions are frequently followed by personal pronouns.

hablé de él (ella) - I spoke of him (her)

Dative pronouns are indirect, e.g., He gives me (indirect) the letter (direct).  Normally a verb does not have an indirect object unless it also has a direct one.

Accusative pronouns are direct, e.g., He sees me (direct).