I'm not an expert, but my suggestion would be to start with a copy of the "Pot ( 4 Gal/15.1 L) - Extract" profile and edit it such that:
- The name is pertinent to you.
Mash tun volume is 8 gal.
Mash tun weight is whatever your kettle weighs.
Boil time is your "default" boil length.
Boil Off - ideally, you'd want to calculate this by boiling a known amount of water for a known length of time and measuring how much you have left. I think the 0.290 gal default here is a bit low (for me it's 0.875/hr, but that can vary widely for different pots), but that's why it's best to measure and get your real number.
Batch Volume is your "default" batch size that you're brewing (presumably 5 gal. based on your kit).
The two loss fields you can set based on your experience or best guess (e.g., how much do you NOT put into the fermenter after the boil and chill, and how much do you NOT rack to the bottling bucket after fermentation).
Top up water is how much you want to be adding to the fermenter to reach your batch volume, if you're brewing extract / partial boil batches.
Any settings not discussed above probably do not need to be touched from the default profile I mentioned up top.
That should get you in the ballpark, for starters. If I'm off-base, hopefully someone better versed in equipment profiles can chime in.