How does a single change in nitrogen base alter the formation of a protein

During translation to RNA, the nitrogen bases on the DNA molecule are translated to complementary RNA bases. Afterwards, these bases are again used to form amino acids.
Three bases make up a codon, which codes for a specific amino acid. If a base is changed, the codon will become changed. This will result in a different amino acid being produced in and the primary structure of the polypeptide will be altered.