Joe, the term "TACK" means to apply the iron tip to a small spot one the covering in order to hold it in place. This way, if it's been tacked down and to feel that it's in the wrong position, you can easily remove and replace it. Once it has been tacked down, and you're satisfied with its placement, go ahead and iron it down completely.

PS no need for glues, there is a heat-activated adhesive on the covering. But do a few test pieces to make sure you have the heat set properly. Too cool won't stick well, and too hot will melt the covering, but you have a pretty broad range in between.