Question

how does the streamlined body help to reduce friction

Answer 1

Streamlining doesn't reduce friction, it reduces drag. In air, this is often called air resistance. However, this effect is present is present in any fluid.

Streamlining reduces air resistance because it reduces the surface area of the moving object that is put under a large force by the air.

Answer 2

When an object passes through a fluid (containing particles, of course), the particles move relative and along the object’s surface. If the object is shaped in such a way that the particles leave its surface suddenly anywhere, a void is created there. This creates eddy fluid currents which could be very random in terms of magnitude and direction.It doesn't. It reduces the drag. It is the air/water resistance offered when you travel through it.

With a streamlined shape, the area of the body that pushes air/water becomes very small. It kind of pierces through the air/water because of the small area that is pushes the air/water while traveling through it. So the air/water that needs to be pushed reduces which means less air/water to push.

This is how making a body streamlined helps cut through the drag.