Hi, great question.

You determine the value of the business before the partner joins, then you determine the value of what they bring.

You then issue new shares to them.

I made this video which may clear things up a bit for you.
https://youtu.be/1EjKjSAd1F8

And this one about share dilution:
https://youtu.be/FtogXYXCC1s

If you want to discuss your specific circumstances, please feel free to request a call.

David
www.DavidCBarnett.com