Where do I find a list of my yahoo groups?

In Yahoo Classic, when you click on Contacts to open your address book, look in the left navigation bar and you will see the titles of your groups in the window on the left.

Click on the Title of the group/category you wish to view.

But, if you need to email them, after you click Compose or Forward, to open your message window open, click on TO, to open your address book that has been set up for emailing. At the top of the list, click on Categories, across from Contacts to open your list of Categories/Groups. Check the box next to the title of the group you wish to mail to, then click on "Insert Checked Contacts."