With the free trial, you can open and edit compositions created by the Vuo community, and use nodes created by the Vuo community.
The free trial has no time limit — but saving, copying, and app exporting are disabled, exported movies are watermarked, and Pro features are disabled. 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, you can activate your copy of the Vuo Editor using its "Help > Activate Vuo…" menu item or the "Activate Vuo" dialog button presented each time the Editor is launched. You can even start editing a composition with the Vuo free trial, then purchase and activate Vuo without closing your Vuo Editor window, and you'll be able to save the composition you edited!