EZ Rotate comes in two versions, one for the Dark Game SDK and one for DarkBASIC Professional. Both versions are included in the zip file you download after purchase.
It sounds like you are looking at the SDK version (which is written in C++). You need to open the zip file you downloaded, then extract the file 'EZRotateEnhanced.exe' and run it. It will then install into DarkBASIC Professional, giving you the new commands you require. A help file will be created on your Start Menu, usually under:
Start - Programs - The Game Creators - Expansion Packs - EZRotate Enhanced
Where you will find links to the help file + lots of DBPro code examples.
Cheers,
Rich
Bite my shiny metal ass