Layers, and why everything depends on them

Photoshop is a layer based editor, and almost every difference between a beginner and a professional is how they use layers.

A layer is a sheet stacked on top of the others. Edit one and the rest are untouched. Flatten them and you have made every decision permanent.

Work non destructively, which is the single most important habit in this course.

Adjustment layers apply a change such as brightness or colour to everything below without altering any pixels. You can change your mind in a month.

Smart objects keep the original data inside, so scaling down and back up loses nothing. Convert a photograph to a smart object before you transform it.

Layer masks hide part of a layer instead of deleting it. Paint black to hide and white to reveal. Every time you would reach for the eraser, use a mask instead, because the eraser is permanent and the mask is a decision you can revise.

Name your layers and group them. A file with forty layers called Layer 1 to Layer 40 is unusable, including by you in two weeks. Name as you go, because nobody ever tidies afterwards.

Keep the layered file separately from the exported image. The PSD is the work; the JPEG is a copy. Clients return and ask for a change, and a flattened file means starting again.

Learn the shortcuts early: brush, move, marquee, undo, step backwards, and bracket keys for brush size. They compound over years.