Leaders connect the fly to our fly line. The leader has a dual function. It dissipates surplus energy from the fly line at the end of the cast. Then we need it to layout our fly the way we want it. When building leaders, we have the heaviest section next to the fly line, and then we tie subsequently thinner and shorter tippet onto the budding leader. This tapering down of the leader helps in dissipation and transfer of energy and turning over of the leader. There are ready-made tapered leaders one can buy (a good choice for novices), and then we can tie them ourselves.
You butt is too small.
Leader series 1-3.