A new Contact record will be created any time that there is a manual entry of account information, either through the front end of a website, or on the back end in areas such as:

Friends Asking Friends
Kintera Golf
Contacts > Individuals

A new Contact record will be established if the account does not meet the criteria established in the Auto De-Dupe settings the organization has in place in Control > Administration > Organization Setup > View/Edit Org Info, otherwise any Contact records entered will automatically be merged into existing records based on the Auto De-Dupe settings.