How do you type square brackets ([ ])?

On QWERTY [ and ] have their own keys, right of P. On Belgian AZERTY in Windows, [ is AltGr + ^ and ] AltGr + $, in the same place.

You use them in quotes, for something you add yourself, and in code.

The keys on each keyboard

On Windows with a numeric keypad: hold Alt, type 91 on the numeric keypad and let go of Alt. Then [ appears.

How are they different from round brackets?

Round brackets ( ) add an aside to a sentence. Square brackets [ ] mark something you add to a quote, and hold lists in code.

When you touch type, you know where every character is without looking. Learn it in short lessons; the first three modules are free.