It’s concievable you could work with Photoshop for a considerable amount of time—-twenty-five years possibly, as of this week—-and still have features that are still a bit of a secret handshake to you. For Photoshop’s twenty-fifth birthday, Deke has teamed with lynda.com to create a series of videos:

What do [mystery Photoshop features] do, anyway?

These videos are free this week in honor of Photoshop’s 25th birthday. Check out the list and click to shine the light of Deke’s insight on any of these curious (but useful) Photoshop features: 

What do blend modes do, anyway?
Blend modes allow you to mix Photoshop layers together in a variety of ways, allowing you to create compositions, colorizations, and other creations by simply changing how a layer behaves with regard to the layers below it.

What do color modes do, anyway?
Color modes—-RGB, CMYK, and Lab—-refer to different ways Photoshop handles the color interaction inside of Photoshop.

What do channel operations do?
Before there were layers and other means of composition, there were channels. And channel operations, or chops, were the only way to make blended images.

What do healing tools do?
The healing tools are one of the primary weapons used in retouching, so for some, they are virtually synonymous with Photoshop.

What do layer masks do?
Layer masks (and their partner, adjustment layers) allow you to reveal only part of a layer, thus selectively revealing the contents of layers below.

What do sharpening filters do?
Sharpening allows you to increase the crispness of the image to really bring out image detail.

What do selection tools do?
Selection tools allow you to choose one element in your photographic image and isolate it from its surroundings.

What do smart objects do?
Smart objects allow you to wrap a protective container around an entire layer of your image, allowing you to abuse it at will whilst keeping the contents safe.

Any other magical, puzzling, or just unfamiliar features you’d like to know more about in Photoshop? Twenty-five years is a long time to collect secret handshakes.