Generally, you'd do that in your personal statement. They give you some characters to describe your EC and what you were required to do in that specific capacity. You're allowed to write a brief description of everything, besides the scholarships, honors and awards you've won.
And what type of "additional information" are you talking about? I know some people on SDN have crazy life stories, about close family members/friends passing away and how their grades suffered, but there's no space for that on the AADSAS app unless you include it in your personal statement. Some secondaries, however, do have an essay for "Additional Information" in which you could include that type of information, that is necessary to your application, but isn't really defined elsewhere. I used the additional info essay as an opportunity to talk about that experiences that explain my background, but because they don't really define me, I didn't talk about it in my PS. I hope this made sense...let me know if I can help with anything else. Good luck!
