Hello Ritbik,
You need to follow some steps:
1) Model the individual components indvidually. This will give you X processes for X products.
2) Make a process called "assembly" or "production" where you add each of the X products as inputs. The output is the assembled product.
3) When you reach the EoL, there is not a button you can push to make the materials go from inputs, into waste streams. You need to model it seperately. Imagine you have 10 materials. You need to choose the flow that represents 1 waste material, and choose the provider that best describes the EoL handling of that waste material. Say:
Waste rubber - Municipal incineration
Waste wood untreated - Burned in boiler
Waste aluminium - Shredded and cleaned for recycling
etc.
4) You can now model your whole product system, using the production of each component, assembly, (use), and disposal of component materials.
Good luck.