Άντε in modern Greek means “come on”, “go”.
It is informal and we use it when we want to urge someone to do something.
Άντε ντύσου, είναι ώρα να φύγουμε! = Come on, get dressed it's time to leave!
Άιντε is an older form, which is also used nowdays.
Άιντε actually comes from the ancient άγετε. Άγετε is imperative of the ancient Greek verb άγω which means “walk”, “march”.