Now that you've seen how to create an assignment, we'll want to take a look at putting that assignment in multiple classrooms, in case you have more than one section working on the same thing.
So, go back to the exercise that you created. (In your classroom, or by going to My Work)
Open the assignment (click the title) and you will see the options to edit, or to clone the piece. Click the little link that says clone.
This will bring up a new page with "Clone of Exercise..." as the title, and the other info all the same. Change the title, make sure your other information is correct, and then select the next classroom you want the piece to appear in. One classroom at a time. You can then provide it a tag.
Cloning your assignments is important, otherwise you will have the same exact node in multiple classrooms, with multiple classes full of students responding to it, and the organization becomes a nightmare. Also, the tagging becomes very jumbled, because the tag from each classroom will be at the top of the same piece. So you may have the same tag multiple times, with each class of students getting "access denied" if they click on the wrong one.