I’m using US terms.

What you can do with them:

If you get fancy you can add cool things in the middle like flowers and stars and circles.  You can also sew them together to make afghans, scarves, placemats, or whatever you want.  You can also continue the same square and make one giant granny square for things like pillows or even a giant single-square afghan!

How to do it:

Ch4, ss in first ch to make a circle.
Row 1: ch5, 3 dc in circle, ch2, 3 dc in circle, ch2, 3 dc in circle, ch2, 2 dc in circle, ss in third ch, ss in 2ch sp.
Row 2: ch 5, 3 dc in 2ch sp, ch1, 3 dc in next 2ch sp, ch2, 3 dc in same ch sp, ch1, 3 dc in next 2ch sp, ch2, 3 dc in same ch sp, ch1, 3 dc in next 2ch sp, ch2, 3 dc in same ch sp, ch 1, 2 dc in next ch sp, ss in third ch, ss in 2 ch sp.

Continue in this manner, making 2 ch between the 3 dc stitches for the corners of the square and 1 ch between them for the sides of the square until your square is as big as you want it to be.  You can change colors between rows if you like.

alternate method:

This method may take a little bit more time, but it keeps large granny squares from spiraling slightly, as they are prone to do sometimes, and really should be just as fast once you get the hang of it.  Click here for this great method!