To import contacts with multiple tags, list those tags in a single column in your CSV file and separate them with a comma.

Your single cell can look like this: TAG1,TAG2,TAG3.

In this case, it does not matter if you choose to use spaces or not in between each of these tags - each of these items will appear as a separate tag for your contact.

Then on the import page you will want to map your tag column with the "Tags" property.