If you wish to prepare your questions before a class, you may create a new Quickfire activity in your class page.
Once you have created a class, on your teacher dashboard, click on the class name and you'll reach the class homepage.
On the class homepage you will see the 'Assigned activities' section as in the following image, click on '+ Create new' to create a new set of Quickfire questions.
You will then be presented with the following screen where you can enter your prepared questions for your Quickfire, you can add as many questions as you like:
Once saved, you will see the Quickfire is assigned to your class, as in the following image:
When you're ready to teach - you can click on the blue 'Teach' button at the top right of your screen. This will take you to the 'lesson' page, where a code will be displayed so that students can join your class.
To launch the Quickfire activity you made earlier, click on the 'launch' button next to the title that you gave your Quickfire activity. You'll then be ready to start receiving answers from the class.