Hi Peri Janis,
Tags are an excellent way of classifying your leads for the purpose of creating email campaigns.
Associating tags to your leads cannot be done when importing directly into the Customer Leads table. When you import a record into the Leads table, Method will automatically create a record in the Contacts table for you. Tags are stored within the Contacts table. You will need to perform a secondary import into the Contacts table in order to assign tags to your Leads.
Have a look at this post (Step 1) - Ben describes the same steps that you will need to do to accomplish this!
We have some further details around importing tags in our Help Center; and also be sure to check out our Import / Export article.
To give you an alternative to tags, you could customize values in an existing customer field (such as the customer type drop down) or add a custom field to the customer table to allow you to further classify a customer. It depends really on how you currently have your company setup. A word of caution when adding additional fields to table - Going down this route would mean you will have to customize additional screens/grids to ensure the new field is available to your end users ... This might end up being more work than using the import/export process as described above.
Cheers