If I understand correctly you want people filling out the form to be able to add formet in the multi-line text field (link links and bold text).
Sorry this is not something that is supported by FormsCentral. Text field and Multiline Text field don't support formatted text.
if they want to add a link they have to type the link and it won't be an active link.
As the form author you can add a link to the form using the Formatted Text Element (look under the Insert menu at the top right in the Design Tab)