Setting Up One Click Registration from an email

You can set up a flow to do this

• Create the Landing page and the email linking to it
• In the smart list use "clicked link in email"
• select the specific email you created 
• add a constraint for "Link" and add the URL that you used

In the flow step you can add them to a list or campaign, send them and alert or whatever actions you need.

You could also use "visited page" and use the landing page url to trigger the campaign. 

One note is you should make sure you have all of the information you need from these contacts already populated in your database before you send to them. 

Do you mean an automatic registration, bypassing the nromal manual form fill out?

There are at least two possibilities:

1. If originating from email, pass the URL parameters along the URL for the landing page.
The form captures the URL parameters to hidden fields.
A small JavaScript submits the form when one of those URL parameters, say, autosubmit=true

2. If totaly random, catering for users clicking email or just reaching the landing page through navigation