Squares and other crochet shapes and motifs with picots at the edges can be joined together at the tips of the picots. Work the first square completely then join on the 2nd. square as follows:-
Step 1: Work the last round of the second square up to the 3rd. corner picot.
Step 2: Work the corner picot up to the centre chain, ( e.g. if 5 chains are required then work to 2). Insert the hook from the back through the centre of the corresponding picot of the first square, work 1 ch then work the remaining chains, ( in this example 2), and complete the picot.
Work each picot along this side of the square in the same way and complete the 2nd. square.
Subsequent crochet squares or motifs may be joined on in a similar way as you complete them, on one or more sides.
Crochet shapes or motifs that are edged with arcs of chain stitch may be joined together in a similar way, linking the stitches at the centres of corresponding arcs.
Shapes my also be joined at the top of any pair of corresponding stitches. Complete a stitch on the final round of the 2nd. shape and work a ss in the top of the corresponding stitch on the first shape before continuing.