Proteins are comprised by amino acids and the order of these amino acids determines the type of protein. This order is coded by the sequence of DNA bases.
Transcription & translation: In the nucleus, DNA is transcribed to mRNA by RNA polymerase. This RNA is small enough to escape the nucleus into the cytoplasm. Here, ribosomes (usually attached to endoplasmic reticulum (ER)) translate the mRNA into a chain of amino acids (peptide). 3 RNA bases (i.e. 1 codon) codes for a single amino acid. This forms the protein primary structure, which is 1-demensional.
Folding: this occurs in the lumen of the ER. The secondary structure is the hydrogen bonds between components of the backbone (diagram to be drawn in interview). The tertiary structure concerns the bonds formed between R (variable) groups (whiteboard). The specific folding patterns are determined by the chemistry of amino acids concerned as well as the chemical conditions of its surroundings. This forms its unique 3D shape which allows it to function.