Simplest Laundry Powder
1 part borax
1 part washing soda
Mix together and use about 1 Tbs per medium load of wash
Powder with Soap
1/2 to 3/4 of a bar of Fels Naptha soap, grated fine (Ivory works well too)
1 cup borax
1 cup washing soda
Use 1 -2 Tbs for medium load
Liquid Laundry Soap
This is more work but some folks are used to liquids. You'll also need a 2 gallon or so bucket or other container to hold the liquid soap. I just used an old plastic bucket from the last bucket of cheap powdered detergent I bought.
1/2 bar Fels Naptha soap, grated
1/2 cup washing soda
1/2 cup borax
Put the grated soap in a saucepan and add 6 cups water. (Put your kettle on to heat up another 6 cups of water.) Bring to a simmer over medium heat and simmer until the soap flakes melt. Add the washing soda and borax and stir until dissolved. Pour this in the bucket and add another 6 cups hot water. Now add another gallon of warm water, plus 6 more cups or so and stir. Let it sit for 24 hours and it will gel up a bit. Use about 1/2 cup per load.
Note: You can also add a few drops of essential oil for fragrance but I find we like the smell of it as is.