Look up two criteria and return correct value - also sum up values after criteria match

Hi all

I have a workbook (sample attached) where i have a column with users and a row with each month and then the number of products they sold each month.

What i want to do is in my 2nd worksheet, i want to have a formula which will match the date and the user name and then return the correct number of products they sold for each month.

I need a formula which will find the correct value even if i change the date in worksheet 2.

I also need a formula to do the above but then sum up some of the months as i require.sample.xlsx

hope the worksheet makes more sense.

cheers