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 a formula such as `=MOD(ROW(),2)=0` for even rows or `=MOD(ROW(),2)=1` for odd rows
Click Format
Choose a fill color
Click OK
Click OK again
To apply to a table, select the range and press Ctrl+T
In a table, enable Banded Rows from the Table Design tab