You want your potential attendees of an event or a membership to agree to a linked waiver or additional terms? You can add a hyperlink to your custom field.
Within Organisation Settings > Custom Fields > Edit Custom Field edit the title and add some html.
It will be something like:
<a href="http://www.workingwithchildren.vic.gov.au">Working with Children</a>
You can copy and past this example above in to your own Custom Field, just make sure to replace the web address it points to and the 'Working with Children' to something more appropriate. Try and keep it the description as short as possible.
You can now add this field to your Event Registration checkout and it looks like: