When you upload a CSV, if you have any Contact Tags included in your file you can map them against your contacts at the Verify your Fields step:

• Click on the Field to save value to dropdown across from your tag column (which will default to show Ignore).

• Then from the mapping field options, under Other select Import As Tags

If you have more than one tag within your column, ensure they are separated by a comma to map them individually. 
You can also can map several individual columns as tags.

If the tags you are mapping are pre-existing in your ActivePipe account, they will be simply allocated to the contact.

If the tags you are mapping are new to your ActivePipe account, a new tag will be created of the same name, and then allocated to the contact.