Once the add-in is installed and loaded through the Add-In manager, you'll find it in the 3D-model tab in your assembly environment, in a panel called Modify Parts. To start projecting holes in your assembly, click the button labeled "Project holes".

Layout
This button will open up a dockable window with a form for all the necessary selections to project holes from one or more components to another. Using the controls in the window, you can pick the holes to project, the face to project the holes to, the termination of the holes and their diamaters.

Pick holes
To pick the holes you want to project, simply click the cursor symbol next to the "selected holes" textbox. This will start the hole selection command. Once hole selection is active, you'll see a tooltip next to your cursor saying "Select holes to project". You can either box-select or single-select any hole or slot geometry from any component in your assembly. while selecting, you'll see the textbox being updated with the number of holes you've selected. To exit the selection, simply move on to another selection in the form or press esc.
You can also clear your selection by clicking the red button with a cross on it.

Pick start face
The start face is the face to which you want your selected holes to be projected. To pick this face, simply click the cursor icon next to the start face textbox. The projected holes created by this command will later reside in the same part as the start face. Exit the selection in the same manner as with the hole selection.

Termination
In the termination box of the window, you're presented with three different options for the extent of your projected holes.

• Through all
  This option extends the holes through the entire part that you've chosen to project your holes to.
  
  
• To surface
  This option allows you to pick a face within the part that you want your holes to be extended to, a so called end face. Pick the end face in the same manner as described for picking the start face.
  
  
• Distance
  This option lets you set a distance for the extent of your holes. Simply put in the desired distance in the distance text box. The textbox accepts expressions and adapts to the units of measure of your document, given that you dont specifically put in the unit (ex. mm, inch etc.) in your distance expression.

Shape
These tools let you determine the diameters of your projected holes. You can either choose to keep the exact same diameters as the holes you're projecting from by checking the "Diameters as original holes" checkbox, or put in your own diameter in the Hole diameter textbox. This textbox also adapts to the units of measure in your document and allows expressions.

Execute the command
Once you're happy with your input you can create your projected holes by either clicking the OK button (executes and closes the window) or by clicking the green button with a plus sign on it (executes and keeps the window open).
Before executing the command you also have the option to get a preview of your projected holes. To see a preview, click the eye-symbol in the bottom right corner.
You can use undo/redo in the Inventor UI to undo or redo the execution of the Project Holes command.

For more information on how to use the addin, see the video: https://youtu.be/q0uChGvcIrs

The installer that ran when you downloaded this app/plug-in from Autodesk App Store will start installing the app/plug-in. OR, simply double-click the downloaded installer to install the app/plugin.

To uninstall this plug-in, exit the Autodesk product if you are currently running it, simply rerun the installer, and select the "Uninstall" button. OR, click Control Panel > Programs > Programs and Features (Windows 7/8.1/10/11) and uninstall as you would any other application from your system.