Don't feel bad. I had problems trying to figure them out when I first started quilting. I bought Lynn Graves setting triangle ruler. I am sure others have come out with similar rulers that take the guess work out of it all. Someone on the board will post sites with videos. If you need to, I would fuse very light fusible where you will be cutting so that you will not have any problems with bias on the outside of your corner triangles. There is a different between setting triangles and corner triangles. Setting triangles have the straight of grain along the long side so there is no bias when you attach a border or binding. They are created by cutting an X in a square piece of fabric. Corner triangles have the straight of grain on two short sides. They are made from one diagonal cut thru a square. Hope this helps. Pictures are worth a thousand words !!!