To add a photo to your post, simply drag and drop it into the editor. Allow some time for it to upload, and you can review all your uploaded photos in Post Gallery drawer.
You can also add free stock photos from Unsplash and Pexels. To open the gallery in editor page, add a new line in the editor, and the toolbar will be switched to add element mode. Click on Gallery button, and the post gallery drawer will slide out from the right.
You can search for specific keyword from Unsplash/Pexels and it will display top results of that keyword. Click on any images, and click Add to Post.
If you have multiple photos, you can simply drag all of them into the editor, and it will automatically create a photo grid for you. You can also create a photo grid from the gallery drawer by selecting multiple images, and click Add as Gallery.