3D Sketch
You use a 3D sketch to define the centerline of the route path.
When you drag a flange or other end fitting into an assembly, a new
sub-assembly is created, and the 3D sketch is started automatically. You
can also begin the 3D sketch manually, if the fittings are already in
the assembly. Right-click the connection point in a fitting and select
Start Route.
Sketch the route path. For pipes, use Line
on the Sketch toolbar. For flexible tubes and electrical
cables, use Line or Spline 
on the Sketch toolbar. Create fillets in the sketch where
elbow fittings or bends are needed.
If you selected the Automatically
create sketch fillets option, fillets are added automatically at
intersections as you sketch. The default radius of the fillet is determined
by the bend radius or elbow you specify in the Route
Properties PropertyManager when you begin in the route.
If you want to add sketch fillets manually (for
example, when you need a bend radius that is different from the default),
use the Fillet tool 
on the Sketch toolbar.
Press Tab to change from one
sketch plane to another.
You can add dimensions and most types of relations
in a 3D sketch, using the same methods as you use in a 2D sketch.
Search for
3D Sketching in the SolidWorks Online Help or see the 3D Sketching tutorial
for more information about working in 3D sketches.