You don't really 'start' a project in the conventional way where you open a program and click 'new project' rather TGEA.exe IS your game, well all of the components in the game that is - what determines what happens, what is loaded etc. depends entirely on the scripts that come with it.
Don't worry, it isn't 100% make game with scripts - you just use them to build game elements, set up players, enemies, NPCs, AI etc. Everything you need (mostly) is in the game executable, that is graphic capabilities, physics, AI logic etc. of course you may need to edit the source code to introduce new things (for example Melee combat. Plus you don't get the source code with the demo) the source code can be opened in Visual C++...good thing though is, Torque comes with basically enough to make a decent game.
As for the level building and GUI, you can open up and editor in your game engine if your editor scripts are present (by default they are) To access the two editors in your game executable, hit F10 for GUI editor and F11 for Mission/Level editor - now the GUI editor can be connected with scripts. (Say you make a button you can type in loadMyMission() into the command property of the button and it'll call the script function 'loadMyMission' which is already define to load the level set in your 'loadMyMission' script (which can be found somewhere)
Scripting is what gets most people with Torque, but it's a decent engine. I've not yet played with TGEA, but I am a proud owner of TGE 1.4.2
I hope that helps.
[edit]
Look around the website for scripting tutorials etc. under TGE and TGEA. Also there is no IDE to open the scripts with Torque - you just open them in notepad or your favourite text editor...of course somebody went ahead and made a Torque IDE that used to be free in its beta stage (it was a kick butt IDE) and now the final version (Torsion) can be bought off of the Garage Games website...if you're trying the demo, best just stick to using a text editor.
I love Nancy DrewG, but not insert brain here