I am not able to understand how to start design with this model file of level 49
Can anyone explain the steps and post the code of two stage differential pair
please help me
Seems you don't care about power consumption and frequency range. You can find schematics of 2-stage differential amplifiers in any Analog Circuit Design Textbook.
"implementing it" means generating it from schematic using a design system + design kit, or creating it manually. If you decide to create it manually, you can get the connectivity from any appropriate schematic; the aspect ratios of the transistors depend on required properties like frequency range (UGB), power consumption, SNR ... and this is your job.