It is a common phrase used to express agreement or to indicate that you share the same sentiment or action as someone else.
Here are some examples:
* "J'aime le chocolat." "Je aussi!" (I like chocolate. Me too!)
* "Je vais au cinéma ce soir." "Je aussi!" (I'm going to the cinema tonight. I also!)
* "Tu es fatigué?" "Je aussi." (Are you tired? I also.)
Note: "Je aussi" is the more common and informal way to say "me too". A more formal alternative would be "Moi aussi".