So you got yourself a COM add-in, and don't know how to use it.
First, you need to set your application up to use them. Go to ToolsCustomize. On the left, scroll down to Tools, on the right, choose COM Add-ins. Drag the COM Add-ins button up onto one of your toolbars.
Once the COM Add-in button is on your toolbar, close the Customize dialog, and click on the COM Add-in button.
Here, you can Add, Remove, check (to load at startup if you use it often) or uncheck (so it doesn't load at startup because you only use it occasionally) the add-in.
If you choose to Add a COM Add-in, you'll be browsing for a DLL file when you hit Add.
Dynamic Link Library. A file that contains several small programs or routines that are common to many programs such as opening a window or saving a file. These library files have a .dll extension.
Source: Microsoft office