It's easy to import your new photos into the Photos App on your Mac.
Option 1: The Import Menu
You can use the file-menu-import option to access any image files contained within your macOS. This may include folders, external hard drives, mounted memory cards, etc.
Option 2: Drag & Drop
If you want to import image files from your finder, desktop, or downloads, simply select, drag and drop them into the Photos icon on the OS X Dock. Then open the Photos App, review your selection, and select “Import All New Photos”.
Option 3. Import Images to an Existing or New Photos Album
Easily import photos into an album by dragging and dropping selected photos. Simply select the ‘Albums’ tab and open the album of choice (or create a new album by clicking the + plus button). Then just drag and drop photos into the album.