Pick a block, lay out the rows, and give every patch its fabric. Put it on the bed to see how it hangs. Then set the real size and take the cutting list to the cutting mat.
Sizes are finished sizes, what you see once it is all sewn. You can type fractions, like 12 1/2 or 3/8.
Keyboard: focus the quilt, move between blocks with the arrow keys and between the patches in a block with comma and full stop. Enter uses the tool. R turns the block, F flips it, the number keys pick a fabric, Ctrl+Z undoes and Ctrl+Shift+Z puts it back.
A quilt you can design in an evening and make over a season. Pick a block, lay out the rows and give each patch a fabric. Turn a block or flip it if it looks better the other way round, and put the whole thing on the bed to see how it hangs over the edge.
When you like it, set the real size. The cutting list adds the seam allowance for you, counts the pieces in every fabric and works out how much of each to buy, with the binding and backing on the end. The printed sheet has a diagram of each block and full-size templates for the triangles, with a check square so you can tell if the printer shrank them. All of it happens here in your browser. Nothing you design leaves the page.
Press your seams rather than ironing them: set the iron down and lift it, instead of pushing it along. Triangles have a stretchy bias edge and they will thank you.