Step 1:

Browse to SharePoint Central Administrator by opening your web browser and going to http://yourservernamehere:12808/default.aspx

Step 2:

Under Application Management, select "Manage service applications"...

Step 3:

Click "Secure store service"...

Step 4:

If you haven't done so already, you will need to generate an encryption key and pass phrase.  SP will warn you that you need to do this and walk you through it.  It's really easy.  If you don't get the warning for some reason, and have not yet generated the key, you can do so on this screen by clicking the "Generate new key" button.  Once you have the encryption key setup, proceed to next step…

Step 5:

Once you have the encryption key setup, it's time to setup the Target Application ID, group, and assign users to the group.  Start by clicking "New" in the menu on the Secure Store Service screen…

Step 6:

Clicking "New" will take you to the Target Application Settings screen.  Fill out the form similar to what is in the screen shot below, replacing the values I've used with your own. Be sure to select "Group" for Target Application Type! Click Next.

Step 7:

On the next screen, leave it the way it is and click Next.  It should look like this:

Step 8:

On the next screen, you add users who should have admin privelges to edit the secure store target application.  You add the users to the first box on the screen. 

In the second text box, you add the users who should be mapped to the group execution account.  In this example you can see I added two domain user groups, and they will be mapped to the group login "vgsdemo" (we setup the group login in Step 6).  When finished click OK…

Step 9:

You will see the generic SP 2010 "processing" splash screen, and after a few seconds if everything is successful, you will see the new Target App ID listed in the secure store service list…