You may find yourself wishing you could divide up your tags into separate categories to make it easier to find stuff. This is done easily enough.
Go back into your classroom, and click on the "tags" button on the top. Now you will see a list of your Tag Vocabularies. (There will only be one, unless you've already created more.) Above that list, you will see "add vocabulary." Click that link, and it takes you to the page for setting up your vocabulary. You'll want to give your tags a title-- such as Tags- Unit One, Tags- Unit Two-- and then you have a few check boxes to select.
"Content Types" refers to what types of content the tags will appear on. You definitely want blog post and exercise, and also wikis.
Scroll down farther, and just like when you created your first vocaulary, you want to check off the bottom two boxes, and click save.