Put on your tank of choice as if it were a skirt. You can either put it below your bust or where a skirt usually would go. (Your waist)
Role the top of the tank top in towards your boddy so it is not showing.
Then get out your belt (preferably without any holes) and fit it around where the top of the tank (skirt) is.
Once you have gotten your belt in place, tuck in the pieces of the tank/skirt that are sticking out above the belt under the belt.
Then enjoy your cute business looking skirt and get on with your life!