On each level of EBONY, you will encounter a riddle of sorts. Solving the riddle will require you to observe what you see, and connect the clues that the creator has carefully left behind. The solution will be a word, number, or a mixture of characters, which will allow you to progress to the next level.
The first few levels act as a tutorial to guide you through the process, but eventually you will be on your own. If you need some additional help, the Getting Started category will contain some useful tidbits.