Inventory question from a newbie!

Hello everyone!

We are very excited to start using smartsheet but we are having some questions with regard to inventory. Here is what I am trying to do:

I receive item 1 in inventory with a quantity of 10g. A few days later, I want to use 2g of that item. How do I use smartsheet to record the 2g was taken and showing only 8g is left?

Any help would be very much appreciated! Thank you!