If you have a Photos library already on your disk, you can add it to your list by clicking the “+” button and selecting “Add Existing Library”, or by selecting “Add Existing Library” from the File menu. PowerPhotos will automatically search your computer using Spotlight for any libraries that are not already in your library list. You can select one or more libraries from the list it displays and then click “Add” to add those libraries to your library list.
Spotlight is not able to search some drives, such as network drives or other drives excluded from Spotlight indexing. If a library you want to add does not appear in the search results, click the “Choose Manually…” button, and that will let you select a specific library to add to the list.