There's actually many different kinds of yo-yo strings. There's mixtures of cotton yo-yo string, mixtures of cotton with polyester, as well as just complete polyester strings. They've even made strings out of all sorts of crazy stuff like nylon. A basic yo-yo string is actually 2 strands of strong twisted together. There's actually 2 strands. When you want to put a yo-yo string on, you actually just take your 2 fingers and untwist the string like so. You'll see the 2 stands will separate. If you open that up like that you can make a loop. What you do with this loop is you open it, hold it with your hands, you take your yo-yo, and this fits around one half of the yo-yo gap just like so. Pull the yo-yo to the side, grab the string, and then you just let it twist right back onto the yo-yo. Your yo-yo is all set to be played with at that point. The next thing you need to know is how to make a slipknot. A yo-yo string has a knot at the top. It looks just like that. It's not going to adjust to your finger like that. What you need to do is take the loop, you put it over the string like so, and you pull that string through the loop. Now it's adjustable and it'll hold on to your finger like so. Then you also want to adjust the string length. You usually want it from your belly button to the ground. This is string is all set for me because it's just about my height. If I was a little shorter, I'd hold it where my belly button was. Tie a regular old knot and cut off the excess. That's the basic of yo-yo string.