Learn Italian: Dove ti sei seduto? - Where did you sit down?

In Italian, all reflexive verbs must use essere (to be) as their helping verb in the past tense, never avere (to have). Since the verb for 'to sit down' is reflexive, we use sei instead of hai.

What is the ti doing in this sentence?

The verb sedersi (to sit down) is reflexive, meaning you literally say 'to sit oneself'. The ti is the reflexive pronoun for 'yourself'. In this tense, it always goes directly in front of the helping verb, which gives us ti sei.

If I am asking a woman where she sat down, does the sentence change?

Yes! Because reflexive verbs use essere as their helping verb, the ending of the past participle (seduto) has to change to match the gender and number of the person doing the action. If you are asking a woman, you must say Dove ti sei seduta?.

What is the dictionary form of the verb used here?

The dictionary form is sedersi (to sit down). The -si attached to the end is your clue that it is a reflexive verb and will require both a reflexive pronoun like ti and the helping verb essere in the past tense.