You'll have to determine what you want your preboil volume to be based on what you boil-off. I have a high boil-off rate in my kettle. I start with 9g for a 60-minute boil and 9.75g for a 90-minute boil. After all is said and done (trub in kettle and fermenter, dry-hopping, etc..) I end up with 5g in the keg.
Once you create the recipe, you can ad a 'batch' for that recipe. That will have instructions and what your mash and sparge amounts should be. This is based on the water:grist ratio you set.