Mikki...cut strips the correct length to match the sides of your blocks and however many you will need to have 1 to go between every 2 blocks...for instance..if your blocks are 12 1/2 "...and you have 4 blocks going across in a row...then cut 3 strips 12 1/2" long by however wide you want them...2" wide sashing???..cut them 2 1/2". (the 1/2" will be taken up with seam allowances on either side)
Step 2...sew a strip to a block..repeat....until your row is sewn together
Step 3...measure the length of the row..add 1/2" to each end for seam allowances..
Step 4..cut your strips for the horizontal sashing...
Step 5...sew the already sewn row to the strip...repeat and your top is done!
Good luck!