copying formulas in spreadsheet for a range of rows

Hi,

can anyone help me how to copy formulas for a range of rows so it reference the correct cells. For example if I add a formula in cell C1 which is SUM(A1:B1), now how to copy it for entire column that C2 has the result SUM(A2:B2) and so on, like actual spreadsheets. I’m not getting this to work.