Layer masks are probably the most significant tool/concept within Photoshop, but for the beginner, they can be a little bit confusing. This helpful tutorial will clear up any concepts that you might find baffling.
Here, landscape and commercial photographer Mark Duffy details the various ways in which to use and manipulate layer masks in order to combine separate layers and/or photos together. Pay particular attention to his use of shortcut keys, because learning these commands early on will save you an enormous amount of time in the long run. His advice on using smart objects for a non-destructive editing workflow is wise, as there are few things more annoying than having to start a complex edit again because you messed up a layer early on.
Smart objects allow you to resize a layer without destroying pixels, but probably their most powerful attribute is the ability to apply certain filters to them. Why is it powerful? Because the filters you apply to a smart object can be re-edited and fine-tuned as much as needed without having to create a new layer. Simply double-click on the specific filter you need to adjust, and voila, the filter's dialogue box reopens. There really are very few disadvantages to working with smart objects. However, be warned: they will greatly increase your file size. This is important to keep in mind if you're working from an external hard drive or if you have a lot of layers in your document.
Did you learn something new about layer masks from Duffy's video?