My content type has a string of words, how do I make them tags? I am very new to drupal. I currently have a content type called 'Issue', which has a plain text field containing something like "money, houses, pigs". How can I look at that string and turn each word into a tag?

The reason I have this is because I read data in from an older database, and they had their tags saved as a string. I read it in using the feeds module. 

Is there a way to read in the tags differently? Or is there a way to parse that string and add each word as a tag in my content type?

Note, I read in the database as a CSV file.

My end goal here is to be able to 'query' for all Issues tagged with the word 'house' for example and display those.

Thanks in advance.
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.