First, chose 20 charm squares, then cut 20 plain white fabric 5" squares.
I sewed a 1/4" seam around all four sides.
Trim your corners (this really does help with the bulkiness where your corners join when sewing everything together).
Now, take you four HSTs and sew two toghether, as below, and repeat for the other two. Iron those seams!
Once they are all done, lay them out in a 5x4 grid that you like and sew the rows toghether.
Now, onto the borders. I decided to use both a dark teal and white border on this one. I cut three 5" strips by width of fabric, for the inside border, and five 5" strips by width of fabric for the outer border.
Repeat the same for the white (you will need to piece together two white strips in order to complete the full border in white).