Contacts can be imported from a CSV and exported again from the header of Contacts.
After Importing
Imported contacts have no behavioural history until the snippet sees them on your site. They will appear in Contacts immediately, but with empty page-view and last-seen columns, and they will not match behavioural audiences until they visit.
Importing Leads
The Leads tab has the same Add and Import buttons. Leads you add stay out of All Users and are reached through the Form leads audience card, alongside the people who came in through a form. Only leads you added or imported can be removed — a form lead comes back the next time the snippet sees them.
Your contact count is a plan limit checked against the live total, and imported leads count towards it too. A large import can push a workspace over its limit — check Settings → Usage against the number of rows in your file first.