If you recorded dark frames and/or flat field frames (cf. concepts : calibration), they will be used to calibrate the images before processing (all your images/movies shall have the same frame size).
Select the kind of calibration frame you want to add, with the mode menu at the top of the window.
Add QuickTime® sequences and/or images as you did for the image list.
When the image list is complete, select the "Stack" tab and press the stack button.
When the calibration frame is stacked, you can select the "Process" tab to visualize the stack, in the image frame on the right of the document window.
Perform these operations for dark frames and for flat fields.
Use the mode menu to go back to image mode for the following steps
You can now go on with the alignment tutorial