Welcome waggus. What you would do is CO (I suggest 2 sts) and increase 1 in each st. Then knit a row plain, then inc at both sides every other row. Do that until the edges are the size you want the square to be then you can practices decreases. Another way to do it is CO 3, knit a row, then inc only at the beginning of every row.
Just for practice it doesn't matter which one you do... do all of them, one at a time. You'll get practice at knitting and increasing and can decide which one you prefer, either because of how it looks or whether it's easier for you to do.
sue- knitting heretic