My content type has a string of words, how do I make them tags?
You can do it using the Feeds module, you probably could have done it when importing the data for the first time. 

Create the Taxonomy you need with all the terms. 

Export the relevant nodes information containing the text field, in the CSV copy the text field column and manipulate it so you can use it to import the terms into a multi-value Term reference field. 

This requires a bit of Excel/Calc magic. It will probably be term IDs separated by semicolons IIRC. 

Then use a Feeds importer to update the existing nodes (the same ones you exported), make sure to map the correct column to the Term reference field for the new Taxonomy.