Put your homemade laundry soap into a jar and you're ready to go. I use a big gallon jar, or if I've made a bigger batch, my old empty laundry detergent containers.
Most folks use about 1/4 cup per load in a High Efficiency (front loading) washing machine and 1/2 cup in a regular (top loading) washing machine. Add more or less depending on your results and your particular laundry needs.
I've had it reported that sometimes the soap has trouble dissolving completely in cold water. If you do a lot of cold water washing, you may want to dilute your soap down a bit further (by adding more hot water and stirring) and using more per load. Or just add a little water to the soap when you're adding it to your machine.
For heavily soiled loads, you can add a bit more borax (1-2 TBS) or some "Oxyclean." Liquid bluing is a good additive to help whites get really white.
Another great tip is to use 1/2 cup of white vinegar as a rinse/fabric softener. The vinegar helps dissolve any soap residue which is what makes clothes stiff. And no, it doesn't make your clothes smell like vinegar...it all rinses away.
Enjoy your new homemade laundry soap. You'll smile a frugal smile every time you walk past the laundry detergent aisle at the market, knowing that you're spending a fraction what those cost, and using a much simpler, less chemical-filled clothes washing alternative.