Notes were added in MC15. They allow you to collect any text information. The Notes section will appear in the tree on the left if it is active.
If you want to try MC's Notes feature, you may need to turn it on in Options/General/Features. You'll then find it in the tree on the left. Just enter any text as a note. MC will file it. Notes can be details of your contacts, and if you tag them as "Google Contacts", you can use the "G" in the upper right corner to sync them to your Google account.
You can search for a note using MC's search window in the upper right corner.
Right click on a note for more options.