that's easy. you can give them the url of your hub and put your referral tracker in it. Normally, your hub link looks like this, http www hubpages com /hub /YOUR HUB TITLE, but if you put your referral tracker it will look like this, http www.hubpages.com /_YOUR REFERRAL TRACKER /hub /YOUR HUB TITLE. (this is spaced because putting in links here is not allowed)
You can find your unique referral tracker under "my account" then "earnings" then "referral trackers". There are a few hubs here explaining that, or you can go to the community page for tutorials and other ways you can use your referral tracker and increasing commission.