The central Dogma states that RNA is created from DNA in a process called transcription, and Protein is created from RNA in a process called translation. The RNA is almost an exact copy of the DNA, except that the letter T (thiamine) is replaced by the letter U (uracil).
These proteins govern everything related to how an organism behaves.
To transcribe DNA to RNA, DNA is unzipped to create a transcription bubble. RNA polymerase creates a single strand of mRNA from the DNA. The RNA is translated in blocks of 3 into the corresponding Protein.
However, we now know that the information can also flow the other way. Proteins that are secreted can actually go and bind to bits of DNA, therefore turning on-off some parts of the DNA. This way cells are able to behave differently — so cells in different parts of your body perform different functions during different times of the day.