Basically, to make beer you have malt, hops and water, then add the yeast to ferment the good stuff in the malt.
What you have in a kit tin is (liquid) malt extract , plus a bit of hops - you can also buy just plain Liquid Malt Extract (same kind of tin, just has no hops added) . The Breiss Light Malt Extract is essentially the same thing, except in powder form.
One kit tin does not have enough sugars in it to make a whole 23L batch, at least not a strong one! The instructions tell you to add sugar to make up the difference, but that is a bit of a short cut (although there are times when adding different types of sugars - dextrose, maltodextrose, honey, molasses etc can give different desired effects).
What Droopy Brew is suggesting is that you use the two tins to provide the required level of sugars - and you get two lots of the included hops by doing that, which isn't much in lager kits, and extra on top would be needed to make an IPA.
That's where Ian's spreadsheet helps to design your brew - you can adjust the variables and get a calculation to see if it looks reasonable.
Hit the blue new recipe button (and make sure you have macros enabled) and select the desired Beer Style at the top of the sheet - in this case maybe American IPA. You'll note the four values on the right are all red because no ingredients are added yet.
Add the two kits you have from the drop down menu. I couldn't see the Mangrove Jacks so I selected a Coopers Bavarian Lager instead. The FG and IBU's now come up green (in the range for the selected style). Then ad the Carapils and Medium crystal in the Grains/adj section. If you ever have to add sugars for your recipe, these are the bottom two lines in this section.
Add in the hops suggested and 10 mins for each. You'll need to boil these - you can choose the amount of water (Boil volume in litres) and add some dry malt extract as you are aiming for the gravity of this mix to be 1.040 to get the best out of the hops. The spreadsheet tells you how much to add depending on the boil amount (or you could use the calculated amount of LME alternatively.
Scroll across to the right of the screen - there is an awesome graph to show the balance of the malt versus the bitterness of the hops to see if you are near the ball park.
One packet of yeast might suffice but adding two increases your chances of success and a good strong fermenting. Aerating the wort is also vital for this.
I found adding recipes from a book to the spreadsheet and seeing how they matched up against the style they were meant to be very helpful in getting my head around the variables. There. are heaps on the coopers website too.
Lastly, don't forget to hit the Save Recipe button! I recon I might give this one a crack next.
