Tap the button that looks like a sack of emeralds on the right side of the main screen:
If you do not see this button, tap the emerald icon in the upper-right corner of the main screen:
Scroll the left list and tap the Emeralds tab. Then press Go for it! in the right part of the screen:
Select an offerwall provider. You will see a list of all available offers. If this list is empty, no offers are available at the moment.