Stock levels

i hope i just attached it,, this is not relevant to the stock project but as you can see from the attached file i can do the v-lookup - i was intending on changing the price data to the stock level. so then i would select from the combo box and it will show me the stock level. However i cant seem to find a way without using vba how to then manage the stock by entering how much of one stock i have taken out (if that makes sense). I intend on then colour coding the stock levels to show severity of stock levels (conditional formatting i think does this colour).
ps. how do i make my combo box's part of the cell , in my attacthed file they float above cells, ive seen people have drop down/combo boxes part of the cell.

thanks

cheers for that link, very useful however it is a bit too complicated for me i cant understand it even after reading the information so therfore i wont be able to do it myself.

ok i dont get:

1) on the catalogue sheet there is two of the same sections , the lower one has widgets and wodgets and the top one has just got wodgets am i correct in thinking its just to show the formula.?

2) =(SUMIF(inv_prod,B10,inv_recd)-SUMIF(inv_prod,B10,inv_used))-E10+F10
when looking at the formula i dont understand the "inv_prod" etc i know where it is from looking at the forumula break down but why is it called this because i cant see a column name?

3) on the inventory page how do they get the inormation to change when the drop down list changes,

4) how does the "update button work"

5) when you press the button how do they get it to so another row appears.


yehhhh many questions. thanks

relating to attachment :

as you can see i have re done a whole new basic spreadsheet as a better example.

As you can see from the attachment there is one combo box and then a stock column (this is the companies stock level). how/what do i use to then have a taking out of stock column - so lets say the stock level is 50 and them someway you then say you take out 5. THis will then be displayed as a current stock level.