You need to create segmentation files for your data. You can use VarScan2 (the copynumber) function, or any other program that computes copy number information. My tool of choice is ExomeCNV though I don't know how supported it is these days.
Then you can add the mutation information (optional). If you call your mutations in VCF format you can annotate them using snpEff, and then convert to MAF format using a tool called vcf2maf.
As you can see there are a lot of steps between having WES data and the correct input data for ABSOLUTE. I am not going to tell you how to generate all the proper files, you can read the help information for each tool.
I think you will find this useful: A: Anyone Has A Working Example On How To Run Broad'S Absolute On Exome Sequencing