Custom fields question

Since there is a way to include custom fields, how do you define what they do and where the data goes?

I want to have a “comments” field, but I can’t figure out what happens to any comments that get filled in there.

Also, is there a way to make that comments field re-sizable? Exactly like the widow I’m tying this into would be great.

Thanks,
Scott

https://www.ads-software.com/extend/plugins/constant-contact-api/