"Girls are pretty."
Translation:Dívky jsou hezké.
please tell me what endings to use for adjectives like why is it "hezké" and not "hezki" or "hezky"
As with your question about demonstrative pronouns in another discussion, the adjective needs to match the noun it modifies in gender, number, and case. See the declension table for hezký at a different, but also useful, site: https://en.wiktionary.org/wiki/hezk%C3%BD.