How does the rna polymerase know which genes to bind to?

In DNA, there are certain specific sequences that the RNA polymerase recognizes as the signal that they are to bind at that point and start transcription: promoters. A promoter usually has three parts: the DNA "start site," the "-10 sequence" that appears before the start site, and the "-35 sequence" that appears before the -10 sequence. The coding at the -35 sequence is TTGACA. One can consider these two pre-sites as a notice to watch for the start site, where the actual binding occurs.