How to post the inventory if i purchase several raw materials like A,B,C, and make the final product X and sell the final product X. how to match the both

It depends

If you buy raw materials and use some, while stocking the rest, then that purchase is inventory items.  If you buy only what you need and use it all up to make the final product then you do not have to stock the raw material as inventory

QBO does not do manufacturing, unlike desktop it does not have an assembly item that does just what you describe.

You have to use a work around
Create a dummy bank account called WIP, create a dummy vendor called dummy

When you purchase the raw material(s), use the WIP bank as the expense for the purchase
as you pay the vendor bill for each stage of the process, use the WIP bank as the expense
If the raw material is in inventory, use inventory adjust, set the adjusting account to WIP, and lower the qty of items being used

that accumulates all charges for the process, when the process is complete
"Purchase" the inventory items from the dummy vendor, and pay for it from the WIP bank, that will zero the WIP bank and stock the items in qty and cost per item