When you choose a photo it opens like this – with the sliders to the right on the default settings.
When you click on the i at the bottom of the slider menu you can see an explanation the effect that each slider has. You can also use crossed arrows to get a series of random effects – this is a good way to explore the effects the first time you use the app.
When you click on the arrow in the top right you choose an image to share or save. You can crop the image, save it to photos, email it or share it through social media.
This is an outline of the basics. There is lots more that this app can do – if you have any interesting results add them to the comments below.