Calculating functions

I am relatively new to database development, my application is simple but i need help.

I have made an application to keep track of gold distribution to my employees. (i work for a jewelry workshop)

I plan to have a form for each of my 5 employees. Each form has a date field, action field (this defines is the material is given to a goldsmith or the goldsmith returns material.), material type (3 choices) and the weight.

My question is regarding reports, or perhaps views. My main objective is to display how much of each material is in the hands of a goldsmith. Now i know how the simple calculation will work. My difficulty is applying this in the application. I need the difference between the total sum of given and returned materials for each material type to be displayed in a view or report. Please guide me in the right direction.