@Fardad
Exactly what are you assembling?
how to lift the machine depends on what your trying to do, what type of machine it is, how much it weighs, etc.

Identify a Lift Point, Prepare the Load for Lifting, and Chock Wheels
Before lifting a forklift with the jack, you need to identify a lift point and prepare the load for lifting.
1. Remove any load from the forks of the forklift and lower the forks to the ground.
2. Identify a lift point at the rear or side of the forklift.
WARNING! When selecting a lift point, it is very important that you consider the following:
* Position the jack so that, as the forklift is lifted, the load will be balanced on the forklift tires that remain on the ground.
* When raising a forklift from one end, always chock the wheels that will remain on the ground.
* Make sure at least two wheels of the forklift remain in contact with the floor at all times. NEVER raise a 3-wheeled forklift from the 2-wheeled end or from the side. NEVER use the jack to raise all four wheels of the forklift from the floor. NEVER raise the forklift higher than 1/4 its tread width