The CAAT box refers to a short consensus sequence of nucleotides in DNA that occur close to (about 80 base pairs away) the transcription start site of a gene in eukaryotes. The transcription start site of a gene is where the RNA polymerase II begins making RNA.
The RNA polymerase II transcribes RNA from DNA, which will then be used by the cells or translated into proteins. It is not able to initiate transcription on its own. The RNA polymerase requires transcription factors, which are a collection of proteins that bind to the CAAT box and form a protein complex that attracts the RNA polymerase.