With the free trial, you can open and edit compositions created by the Vuo community, and use nodes created by the Vuo community. You can explore many of the things Vuo can do by trying out the included example compositions. If you want to dig deeper, you can review the manual, read the node documentation, or watch a tutorial.
The free trial has no time limit — but saving and copying a composition is disabled, app exporting is disabled, exported movies are watermarked, and Pro features are disabled. You can save images and data. The free trial does not include the SDK or the source code (but you can get the 1-year-delayed source).
After you have purchased Vuo Pro, you can activate your Vuo license using its "Help > Activate Vuo Pro…" menu item or the "Activate Vuo Pro" dialog button presented each time you launch Vuo. You can even start editing a composition with the Vuo free trial, then purchase and activate Vuo without closing your editor window, and you'll be able to save the composition you edited!