Didn't even post this in questions, so you could not bother giving me thumbs up anyway.
Those questions suggest to me that you don't understand what you know.
A query to total stuff up is just a query like any other.
"Select Sum(SaleValue * SaleQty) as TotalSales From Sales Where DateOfSale = GetDate()"
So if you can do select * from Sales, you can do somthing like the above.
If you can't then you ned to google and find out, it's not hard.
If are SQL you are struggling with, then there are some good tutorials out there, again find from google.
Changing a database value is just another query, an Update statement e.g.
Update Item Set ItemQty = ItemQty - 1 Where ItemID = ....
When you execute the Command, pick the method that expects no results.
A bit of effort and you could have answered this yourself in about ten minutes given some background knowledge. If you want to make a go of it as a developer, you need to exert yourself a bit more.