Rosalie - You can do it! The biggest problem I had when casting on was figuring out what 'spin your needle 180 degrees' meant. Which part did you get stuck on? Maybe I can help. I'll try to explain the cast on:
When you cast on you'll be holding the needle up and down so that the two points of the needle are facing North and South.
Put your two slip knots on the needle. Yarn A's slip knot (with the working yarn on the right side of the needle) should be put on the needle first so that it sits below yarn B's slip knot (with the working yarn on the left side of the needle). (Took me a minute to figure that out cause in the article it doesn't show you which color yarn is which letter in the example)
Now make your first cast on stitch with color A and put it on your working needle on top of your current yarn B so that now you have three stitches A, B, A on your needle. Make sure the new stitch you just put on your needle has the working yarn hanging off the needle on the right side. (Your one B stitch still has the working yarn hanging from the left side)
Ok, you're still holding the needle up and down in the same position. Now you're going to flip your wrist to the left so that the working yarn from yarn A is now on the left and the working yarn from yarn B is on the right. Knit with yarn B and put that new cast on stitch on top of the stitch you just made with yarn A.
Flip your wrist back to the right so that all the working yarn from yarn A is on the right again and the working yarn from yarn B is back on the left side of the needle and make a cast on stitch with your yarn A.
Keep going slowly back and forth until you have cast on the total # of stitches that you want. In the end it sorta looks like a caterpiller.