The central dogma
Transcription occurs when DNA helicase unravels the double stranded helix of DNA so expose a particular gene coding for the wanted protein. RNA polymerase and transcription factors then bind and start to create a complementary single strand of mRNA. This mRNA contains complementary base pairs (with the exception of Uracil being swapped for thymine) however, it also contains introns (non coding regions of DNA) which are then cleaved out of the mRNA by a spliceosome leaving a mRNA with exons only. The mRNA then leaves the nucleus and attatches to a ribsosome. Every 3 bases on the mRNA strand code for one specific amino acid which is brough to the ribosome by specific tRNA molecules. Once 2 tRNA molecules (coded for by 6 bases on the mRNA strand) are brought to the ribsome a peptide bond will form between them, and as each amino acid is coded for another is added to the primary sequence of the coded protein.
This is what makes up the basic principle of the central dogma. DNA codes for mRNA which codes for a protein.