I've tried a lot to make a 3D model of frustum of cone but have been unsuccessful. How can I model one?
You can simply add a Cone primitive and adjust the radius of the top (Radius 2) and then adjust the length and or bottom radius as needed.
Starting with a default primitive of a cone and a cube from the add object menu. Place the cube so that it covers the tip you want to cut away.
Add a Boolean Modifier to the cone and set Object to Cube and Operation to Difference. After the modifier is applied you can remove the cube:
Start with a Cylinder select the top face in Edit Mode and scale the tip S.