You use a "Y" seam. Start 1/4" into the seam and Stop at 1/4" from completing the seam and lock your stitches. Then add the next piece and use a 1/4 " seam. With each new piece you add stop 1/4" before the end of the seam and lock your stitches. I usually graph out the quilt. Then I turn the graph paper 1/4 quarter turn and piece the hexagons in rows. These will all be straight seams. I still stop 1/4" before the end of each seam and begin 1/4" into the seam. This give you the room in the seam you need for joining the rows. Once all the rows are pieced and laid out in the correct pattern you should join the rows using the same method. It takes some time but it is lots of fun and very relaxing.