I am brand new to CiviCRM and trying to clean up a very messy database. I read the user guide for deduping and merging, and it made it seem like this is a built in feature I should find under contacts, but I do not have that option? Thanks
There is a CMS (e.g. drupal/wordpress) permission for
CiviCRM: merge duplicate contacts and you also need "Delete contacts" permission. Does your user account have those permissions?
Also try it with a search for contacts, and then from the Actions dropdown on the results page there is an option to merge contacts.