Blending modes are one of the most foundational features in Photoshop and something that almost anyone working with the program should understand well. This in-depth video will show you the ins and outs of every single blending mode, allowing you to better understand when to use each one and how they can help you achieve your desired results.
Coming to you from Unmesh Dinda of PiXimperfect, this great video will show you everything you need to know about blending modes in Photoshop. Blending modes are so essential because they tell Photoshop how to combine different layers. At the most fundamental level, blending modes are simply mathematical equations that tell Photoshop how to take luminance data (and sometimes some other data) from two layers and combine it to get a single result. This can be something very straightforward, like simply taking the brighter of the two values, or it can be something much more complicated, light normalizing and multiplying individual channel values. While you certainly don't need to become intimately familiar with the math behind blending modes, it's important to understand how each operates and have an intuitive feel for how they'll affect an image, as they're one of the cornerstones of editing in Photoshop. Check out the video above for more.