How does rna polymerase know where to start transcribing a gene?

Transcription factors (activators and repressors) bind specific sequences on the
promoter. Activators allow RNA polymerase access to DNA. Repressors block RNA polymerase access to DNA Nucleotide sequence of promoter (and therefore which proteins can bind) determine WHEN (developmental time), WHERE (which cells) and HOW
MUCH RNA the RNA polymerase transcribes.