Inversion forms a question by swapping the subject pronoun and the conjugated verb, joined with a hyphen: tu parles becomes parles-tu? (do you speak?), vous êtes becomes êtes-vous? (are you?). It's associated with more formal or written French rather than casual conversation.
When the verb ends in a vowel and the subject is il, elle, or on, an extra -t- is inserted for pronunciation: il parle becomes parle-t-il? (not parle-il?), va-t-elle? (not va-elle?). Inversion with a noun subject (rather than a pronoun) keeps the noun in place and adds the matching pronoun after the verb: Marie parle-t-elle français? (does Marie speak French?).