To put a block (or blocks) into a border, choose a
block you want to use in the border, from the block library and add it into your sketchbook .
Open the quilt you are working on, and go to Borders in the lower left tab, dial in width, and number of blocks per border, this can be altered, once you have seen the effect when you put the block in.
Go back to layer one tab and move the block you chose from your sketchbook into your borders. If you don't like the look of it,perhaps because it is too stretched out, or too squashed, go back to the border tab, and alter the width of border, or number of blocks, until you get the effect you want. That should do it.