Importing Contacts; is an Account created automatically or do I need to create the Account first?

I'd like to import all the our Contacts, some of which are associated with an Account. Do I need to establish the Accounts first, and will Zoho somehow match those Accounts with the Contacts, or will Zoho create an Account if I state an account name while importing?

On a similar note, what's the difference between importing as;

Import My Contacts

Import My Organization Contacts

I'm assuming that I should import all my Contacts as 'my organization contacts' (even those that don't have an account) or would I be best to import only those with an associated Account as 'my organization contacts' and my other contacts as 'my contacts'?

Thanks in advance! Sofia