There are two easy ways to create a project with wireframes. The first way, is to create a new project from a template.
Once you log into the Definition Center, select the 'Create New Project' button from the Dashboard in the top right corner.
You'll have a few options in the next popup, including choosing a template. I would suggest using the UX Toolkit, (don't forget to give you project a new name!)
Another way to create a project with wireframes, is just changing the widget library in an exiting project. There are a few options you have, that contain widgets to make your life easier for you.
From the Edit tab of your project, select the 'Widgets' tab, and then change the selection option. Normally the default widget library will be 'Basic Widgets'. I would suggest either of the 'Diagramming' libraries, or maybe even the 'Wireframe Templates and Toolkit' library. Of course you're not limited to just those libraries, feel free to check them all out.
Once selected, just pick a widget, and drag then drop to your page. That's it!
As always, please contact support if you need further help.