First things first, make sure you're in your Profile.
In the Education section, click on the Add (+) icon in the top right corner.
A drawer will slide out from the right for you to fill out the information.
When you're all done, click Save to save your changes.
Voila, it should look something like this:
To cancel any changes you've made, simply click the left arrow in the top bar. You will be prompted "You have unsaved changes. Are you sure you want to leave without saving?" Just click 'OK' and your changes will not save.