You can get to your counselor list using the Manage badge menu. Click on the Manage badge, select Members, then Merit Badge Counselors as shown below:
Here's what the counselor list looks like:
Anyone who counsels a merit badge will be included on the list. So how do you add a merit badge? Just go to their profile from the Manage badge or using the People option from the powerbar, which I show below:
From the user profile, locate the tab labled MBC and select, like so:
Once in the tab, select the Edit button. A very long list of merit badges will appear. Check the box next to each one counseled by the member and click the save button at the very bottom. This member will now be on the counselor list.