Actually, you don't make soap from soapwort. Not bars of soap as we know them. When you swish the roots of soapwort around in water, it sort of foams up. Not as foamy as with normal soaps or detergents, and the foam settles quickly, but it's there. So really, you just use the water in which you've swished soapwort to wash yourself, your hair or your clothes. Simple as that. You actually don't have to rinse out afterwards, though you might prefer to. It's excellent for washing delicates like lingerie or baby clothes, gives your hair a good healthy shine, and is good for a range of skin conditions.

You can, of course, include the soapwort water in a recipe for soap bars if you choose to.

Take my word for it. If you plan to use soapwort water as your preferred washing medium, you'll need LOTS of soapwort. Luckily, soapwort being a groundcover which can get out of control, that shouldn't be too much of a problem after a while!

Here is a link that might be useful: soap plants

I wanted to use it exactly for my hair as a rinse. Good advice. Thanks!

you can also add different things in the hair rinse to give it a nicer smell, or different things to your hair. If you happen to be a blonde you can put chamomile in it, or lemon juice to lighten and give a nice shire3 to your hair. you can experiment with it. I like to add mint to mine it makes me smell nice. lavender would probably work too. but the more things you add you might need to rinse afterwards.
good luck.