1. Open up Construct 2.
2. Click the C2 icon at upper left.
3. Click on About.
4. When the window pops up, click on View License.
It should read: "This is a standard license, for independent use by the above named individual up to an associated use revenue of 5000 USD, or educational, charity or otherwise non-commercial use. Use outside of these bounds is prohibited."
As I understand it, go ahead and use the artwork, sound assets, etc. As long as you make 5000 USD or less and are not part of an organization/company.
And you cannot use C2 graphics in say RPG Maker VX Ace or GameMaker (and vice versa, obviously).
Check this out too:
http://www.scirra.com/forum/can-we-use-assets-from-the-asset-pack_topic55968.html