Select the range of cells you want to format
Go to the Home tab
Click Conditional Formatting
Choose New Rule
Select Use a formula to determine which cells to format
Enter the formula `=MOD(ROW(),2)=0` for every other row starting with even rows
Enter the formula `=MOD(ROW(),2)=1` for every other row starting with odd rows
Click Format
Choose the Fill tab
Select a color
Click OK
Click OK again