A common use case is to mail your contacts with a link to a form. For example, to ask for feedback or to send an invite. You would like those links to be personalised, so the form entry gets attached to the contact that received the mail (so you know who filled in the form). We call this personalised or auto-login links.
How to create a personalised link
Good news! One Community automatically recognises links that point to a One Community website. Do not forget to put the access level of the page to 'Logged in' contacts. If you have a link you would like to personalise, then you can add this link to your mailing just like any other link. One Community will automatically append a unique login token to the URL to identify and login the contact when he clicks on the link.
You can verify that One Community properly recognised your links, by checking which auto-login links are detected. Refer to the yellow padlock in the 'Content' section of the mailing: