First, I think you need to go to Options/units/Batch volume units and select barrels. Once you've done that, select the appropriate volumetric volumes you want to use for hops, yeast, etc. There are also some other options you may want to change from default values. Next you want to set up an equipment profile that closely reflects your brewhouse. After that, set up some mash profiles. The profiles will likely need to be tweaked over a few batches to get them dialed in.
That should put you on the right page.