If the DNA molecule is only composed of four possible nitrogen bases, how can thousands of different proteins be formed from such a limited set of fixed shapes?

nucleotides are only building blocks whose combinations determine different codons which subsequently associate in a sequential manner in order to create different amino acid combinations

Explanation:

A gene is a specific segment of DNA whose (nucleotide) sequence is copied into an RNA during the process of transcription, typically a messenger RNA (mRNA) molecule which is subsequently used to synthesize a protein. During translation, each triplet of nucleotides, i.e., each codon, corresponds to a specific amino acid.  There are 64 possible codons (4³: 64), which can combine in different ways to create different amino acid combinations, and thus they are responsible for the generation of a huge amount of proteins coded by a given genome.