When does a person gets cookied

When does a person gets cookied

Hi,

we are currently shifting from marketo towards Zoho crm, and we will upload 50.000 contacts in our database.
Which actions can one do so that he/she gets cookied, and will be connected to the stored email address in zoho CRM?
Form Fills? Click a link in an email? Other?
Can one see how many leads/contacts are cookied?

Bye