To upload photos, click on a person. A sidebar will appear, and on top of it a button "Add photo". Clicking on this allows you to select a file from your device. After choosing a picture, click on "Upload", wait a few seconds until the photo is displayed on the sidebar (otherwise the upload action gets cancelled), and you're done.
If you want the picture to be displayed on the tree (instead of being just available when you click on a person), you need to check the box for "Photos" in the "Options" sections on the menu on the bottom of your screen.
Adding multiple pictures per person is - as far as I know - not possible.
Hope this helps!
