Hi all.

I am trying to understand the mutation frequency to annotate my exome sequence data.

Since I look it up on the Internet but I tried to fail how to calculate it.

To make it matter worse, I didn't know the actual meaning of mutation frequency (Wiki seems to explain their definition but I didn't get it..it is too formal) and why this information is important when analyzing mutation.

Could anyone tell me a little bit about their basic meaning and equation to get it?
Frequency is just a count. It is usually normalized to some fixed unit of time or space to enable comparison with other counts. Mutation frequency can conceivably refer to many things depending on the context:

 - Number of mutations per sample/per Mb/per gene, etc
 - Number of samples in which a particular mutation is observed
 - Percent of reads that support a particular mutation
 - Number of mutant alleles in an individual or population (usually called "allele frequency")

Really, you need to define for yourself what it is you want to calculate. The calculation itself should then be straightforward.