The dogma goes like this DNA -> RNA -> protein
Mutation is change (errors) in the sequence of a DNA molecule that is caused by a number of factors. Some mutations can be caused by radiation (ex. UV radiation can cause bulky pyramidine dimers). Tautomeric shifts can cause bases to mispair. 5-bromouracil can mimic bases and cause mispairing. Insertions and deletions can cause an entire shift in the DNA reading frame. etc...etc....etc....
When a mutation occurs in in the germ line (a gamete) it can be passed to offspring.
When mutated DNA is transcribed into RNA it may be translated into a different sequence of amino acids (building blocks of proteins) than the original molecule was capable of coding for. These new proteins may hold a slight selective advantage for an organism and would therefore be passed on to offspring with greater frequency. It should be noted that almost all mutation is deleterious and some is neutral. Most is NOT positive or advantageous.
~ Tad Wood ~