See this article for general API requirements.
In order to pull contact data from VoterVoice, you will want to use the Search Contacts get. You can search by contact ID, email address, or the date last modified.
If you are looking for modifications, you can specify the source of the change to pare down your results. So if you are only interested in changes the users made themselves from the user site, you can include a parameter under the date modified for changedSource=UserSite. Other options for the changedSource are AdminSite, Api, and System.