Inventory managment

the question is, if you can have your inventory manegement in the same
web,
for exemple, when entering a new product, you could asign a number that
you have to sell, and that you can add more, another exampli, if I have
three monitors, and I buy 2 more to sell, then i would have 5, what I
mean is if in tha same web page you can have an inventory system, that
way you and your cliente knows, if your are running out of items,
I tryed to explain, at least I tryed