Method for calculating Invoice Totals and Grand totals

HI...good day..

i need help...not familiar with excel formula and vb..

1) How i want to do Auto Invoice numbering..
2) How do i calculate from different sheet .

here i have one workbook=

1)Invoice =

2)Invoice2 =

3)Summary =(taking from invoice -all have 9 item)

4)grand Total= (calculate from summary)

can anyone help....