Digital art and design

A raster (or bitmap) image is made of tiny squares of colour called pixels. Photos are raster images. If you enlarge one too much it looks blocky (pixelated).
Resolution is the number of pixels in an image, or how many are packed into each inch. Printing usually needs a higher resolution than a screen.
A vector image is made of shapes described by mathematical paths. It can be scaled to any size without losing quality, so it is used for logos and fonts.

Screens make colour from light using RGB: red, green and blue. Mixing all three at full strength makes white (additive colour).
Printers use inks: CMYK, which stands for cyan, magenta, yellow and key (black). Inks absorb light (subtractive colour).
This is why colours on screen can look different when printed.

Useful tools: layers (separate parts of an image that can be edited on their own), undo, selection tools, brushes that imitate real media, and filters.
Work non-destructively: keep the original and use layers, so you can always go back.
Save in suitable formats: JPEG for photos (smaller files, some quality lost); PNG for graphics and transparent backgrounds (no quality lost).
David Hockney (British, born 1937) has made many drawings on an iPad.
Copyright protects artworks. In the UK, copyright in an artwork usually lasts for 70 years after the artist's death. Use your own photos where you can, and credit any sources you use.