Oke so you have Alcohol opened in front of you and on the left you have a panel of options. Under "Options" there should be a link for "Virtual Drive". Click that. A settings screen should come up and the very first option is "Number of virtual drives". Change this to however many you want. 1 is a normal choice. Then click OK and wait till Alcohol adds that. Now on the empty white space at the top right click and choose "Add Images". Here choose the path to your image and then "Open". Then just double-click that file that was added and it will mount it to the one and only virtual drive (assuming you chose 1 for the first option).
Please post back here about what happened and what you would like me to clear up for you!