This is everything I used to make 2 gallons of laundry detergent. The empty milk jug is so I could measure the water, a pot for cooking the ingredients, a small cheese grader, one bar of soap (any soap is fine), one cup of borax, and one cup of washer soda. The borax and the washer soda can both be found at the grocery store in the cleaning isle.
First I graded the entire bar of soap into the pan. Added bonus is it's a pretty good workout for your arms. I used a very fine grader since it all has to dissolve in the water. After the soap is graded I just add one cup of borax and one cup of washing soda and then one gallon of water. I use hot water which is enough to dissolve everything pretty much on it's own, but just to make sure it's good and mixed I boil this on the stove.
I turn it off once it has a good boil and while it is heating I stir it up every now and then to make sure the ingredients aren't sticking to the bottom of the pan (they will).
Once that is done I let it cool some and then pour the pot into a cleaned out container that originally held cat litter. I add another gallon of water and leave it out to cool. 24 hours later it has a slimey soap gel on the top that I just stir up again. I use a cup of it per large load of laundry. It works just as well as the stuff I had been buying and I have 3 times as more for much much less! I don't plan to buy store brand detergent again.
EDIT: I have done several loads of laundry so far and it's hard to tell if it's doing anything at all. My clothes don't smell bad, but they don't smell like anything really. The detergent certainly does not get stains out that's for sure. And since my biggest issue is dog hair- which no detergent is going to get rid of- it's hard to tell if any improvement is from detergent or having the clothes spinning around in plain water. I really wanted this to work, but are the thrilled homemakers online happy because they found a cheap resource or are they just seeing what they want to see?