Here is the tutorial.
Start SolidWorks and open the attached assembly.
Choose assembly features>>belt/chain.
Select the circular face of the both pulley.
Click OK. When we rotate one pulley other is also rotated because of the belt.
Edit feature the belt.
Check the create belt part.
Open the belt1 part.
Extrude the sketch using thin feature.
Switch to assembly window and click yes to rebuild.
Now we have belt created.