Hello Tiina,
an 'unknown visitor' of a marketing page is tracked and the visit recorded, but it could not be associated to an existing contact. This happens if there is not visitor cookie on the visitors device that would allow this association.
As soon as this visitor though submits a marketing form through a landing page, then the submission will try to match the visitor to an existing contact based on the matching strategy. Now the previously anonymous visits will be attached to a previously known contact.
If the contact matching did not identify an existing contact, then a new contact / lead will be created, and the anonymous visitor move into the known contact though this path.
