1) Place slip knot on hook. Place two squares wrong sides together (right side facing up towards you of your front square). You will be working on the right side. If you prefer, you can lay them one next to the other, right sides up. Insert hook in center chain space, going through both squares, join with a single crochet.

2) ch 3, insert hook in next space (in this case it is a ch-1). Work a single crochet in that space

3) ch 3, in next space work sc, ch 3, in last space (your corner) work sc, do not finish off. If your square is larger you will do more (ch 3, sc) across, finishing in the corner.

This photo shows your two squares laid flat, at the same position as the previous step.
 

4) take your next two squares and lay them back sides together, just as you did with the first two squares. Your last stitch was a single crochet in the corner space. ch 3, then insert hook in corner space of your new squares, going through both squares. Complete a sc.

5) (ch 3, sc in next space) 3 times (or however many times it takes to get to your corner space). Your squares are dangling loose because you are joining the rows. You will be going back later to catch the columns.

Here are the same squares laid out flat after completing step 5.

You will add as many squares as are needed for that row in the same manner.
 

6) Begin row 2 just as you did row 1. With wrong sides facing, join with a sc in first corner space, going through both squares. Work (ch 3, sc) across, adding additional squares as available.

7) Once all your rows are done, you need to connect your columns, which are presently hanging loose. You're going to begin in the same manner as before. Be sure you are working with wrong sides together, or both right sides facing up, if working flat. Join with a sc in corner space of both squares

This is a close-up of the same join as in step 7.

8) When you get to the corner space, you will note that this is where you joined your row previously. You will make the sc in the corner space of your first square, ch 3, then make a sc in the corner space of the second square.

Here is a close-up after the join is made

9) Continue across just as before, working (ch 3, sc) in each space. Work the previous join as in step 8.

10) Move on to the next column or row and work as before. You can do this as many times as needed