In elements organizer right click on the thumbnail of the video you want to edit and select "Edit with Premiere Elements" option. This will open Premiere Elements with the selected clip on the timeline. Go to the "Edit" tab and start editing.
You are in the Elements Organizer, which more like a catalog manager and not a video editor.
One of the ways to start editing is as mentioned by John in the post above.
The other way is to launch Adobe Premiere Elements directly which can be done simply by clicking the desktop icon and selecting new project option
OR you can run the AdobePremiereElements.exe from your install location.
I see that you have installed the tryout version for Elements 8, that is last year's version, Elements 9 is already out, its better that you try the latest version. A lot of us on the forum have started using it.
Meantime, for a basic understanding of the program, have a look at my free Basic Training with Premiere Elements tutorials on Premiere Elements support site Muvipix.com.
I've also published a number books, based on my 6 years here as forum host, to help people learn the program inside and out. They're available on Amazon.com and at the Muvipix store.