Twirling seams flattens out some of your seams and so reduces bulk in a four square patch. Here's what I did on a Dear Jane triangle block.
1. Press your seams all toward the dark - in this case, the green.
|right side of fabric (please excuse the bad lighting)|
|wrong side of fabric with seams pressed towards the dark (green)|
3. You need to pick out the 2-3 stitches on your vertical seam that are in the seam allowance of your horizontal seam (blue arrow). The pink arrow is the vertical seam. You will pick out stitches directly above (north) of the intersection of the arrows. Pick them out on both sides of the fabric.
4. This is where I used to get messed up. Open up your fabric. The seams will fall open in the way they will want to lay (sometimes you have to help them a little).
|Starting to fall open|
|I helped them fall open|
|You can fingernail press along the seam to help|
5. Press. I press this seam from both sides because I think it lays flatter.
Here's my finished Dear Jane triangle
|back side of the triangle|
|back side of another twirled seam square|