Appearance differences
Male bettas are commonly sold with longer fins and brighter display forms. Female bettas can be colorful too, but many have shorter fins and a rounder body shape.
Behavior differences
Males are famous for territorial behavior, but females can also be aggressive. Never assume a fish is community-safe only because it is female.
Care is mostly the same
Both males and females need a proper tank, gentle filtration, warm water, cover, and careful feeding.