First, think of something you need to do, then tap on the + button in the app and fill in the details.
If you find the app's large set of features to be overwhelming, you can simplify very easily. In the settings area, tap on "Fields/Functions" used and choose one of the options.
You may also want to familiarize your some basic principles. Because the app is designed to synchronize with Toodledo, you may find Toodledo’s article about the Getting Things Done methodology to be very useful. The information here can be applied to Ultimate To-Do List, even if you don’t use Toodledo.