employee sales

I need to produce an employee sales table that is linked to the employee table. This sales tables need to be able to work out commission.

Information needed is: employee target, month, sales achived, commission allocated (%). All this data is to be entered into this table via a query to calculate commission each month.

So far I have:

tblSales - salesID, EmpID, Date, Order, Price, Qty

do i need to add or take out any fields? also how would I go about making the query.