I am creating a new custom button or link, and when i try to use a Visualforce page my content dropdown list is empty. How do i get a VF page to trigger on a custom button or link.
You need to ensure your Visualforce page uses a Standard Controller for your object.
For Detail Page custom buttons...
For List View custom buttons...
<apex:page standardController="Account" recordSetVar="accounts">
Then Salesforce will display your pages in the drop down list.
You can read a more detailed walk through and some security considerations here.