In spanish what's the difference between direct object pronouns and indirect object pronouns

Direct object pronouns are used to replace direct object nouns, but indirect object pronouns are used to replace nouns that act as indirect objects. Also, indirect object pronouns answer to questions such as: to whom? or for whom? about the verb, but direct object pronouns answer to questions such as: whom? or what? about the verb

Doble a la derecha" means; "turn right" how does "siga derecho" mean "go (or follow) straight"

Imight be able to but were is the picture