Self-taught beginner about to start my third project and there are some symbols in the chart I haven't come across before. I'm guessing that they mean I have to use two colours, but I'm not sure if I just have to mix a strand of each, or if I have to do two stitches in the square (although what type I don't know!). I attach a photo with example squares highlighted. It's an Anchor kit if that makes any difference. Any advice please?