1) Genes encode proteins. (Remember that a gene is a string of Codons that work.)
2)Proteins govern the development of inherited traits. (What makes us...us!)
3)A variation in the DNA sequence of a gene will often express itself as a variation in the proteins that it controls. This in turn, causes variation in the traits contolled by those genes and proteins.
If you will, this becomes the three basic principles to the understanding of mutation:...DNA...to protein...to inherited trait. Simple, yes?