Start with the right equipment. I see you have a mash/lauter tun. You need a big brewpot, because you will be starting with about seven gallons of sweet wort and boiling it down to five or so. That is assuming you are making five-gallon batches.
Before I bought my fifteen-gallon pot I used a six-gallon and a four-gallon, then combined them when they had boiled down sufficiently. Hops went into the weaker wort.
I brew indoors on an ordinary gas range; my fifteen-gallon pot fits neatly over two burners.
One other thing you will need is information for your calculations. Here are the most helpful AG calculations, IMHO:
Strike Water Temperature = (0.2/R)(T2 - T1) + T2
where:
R = ratio of water to grain in quarts per pound
T1 = initial temperature of the grain
T2 = desired mash temperature.
On a recent brew day, I had 10 pounds of grain, stuck a thermometer in it after milling and found it was 69 degrees Fahrenheit. I wanted a ratio of 1.6 quarts per pound and a mash temperature of 153 degrees.
0.2 divided by 1.6 quarts/1 pound = 0.125
153 degrees minus 69 degrees = 84
(0.125) times (84) = 10.5
10.5 plus 153 = 163.5 (or, rounding up, 164) degrees for strike water. So my strike water was 164 degrees.
The above formula is from John Palmer's How to Brew.
Two other things:
1. Preheat your mash tun with a gallon of boiling water, then drain it.
2. You will lose one-half quart of water for every pound of grain. If your total water, both strike water and sparge water, is, say, 30 quarts, and your grain bill is 10 pounds, then you will end up with 25 quarts of sweet wort at the beginning of your boil.
3. Plan to lose about a gallon and a half to two gallons during the boil.
Okay, that's three things. I'm bad at math. But even I can understand the basic equations of mashing.
Good luck!