Welcome to the forums!
Maybe this will help. Each string has multiple threads, but they are intertwined to make 2 bunches spiralling around eachother. Now if you untwist the end of the string, not where it goes on your finger, you will see just one string, a loop. This is the part you put on the bearing. Now to make it more responsive, you want to double this loop over, and then put it on the bearing. If you do it correctly, your yoyo will be more responsive. Its is tough to describe the actually doubling of the loop without a diagram, but I believe it will become apparent after you experiment