Thank you for the feedback! The goal is to find humans in the map and take their souls. When you are near one hold space until they turn into a zombie and then run quickly towards the statue to fill in the souls bar on the top right of the screen. If you are hit a few times the soul goes back into the human and you'll have to try again. You win once all 4 human souls are collected.
Regarding the screenshots, once you upload them to the project you need to go the game page and click the Edit Theme button. Over there you should see an option to show the screenshots dropdown.