Formatting Spreadsheet

How do I shade every other line of part of my table in a grey color without
selecting each line individually?

One way:
~Insert a new column and number each cell in that column, 1 thru X.
~Insert a new column next to that with the formula =MOD(cell
reference,2) that references each numbered cell. This will result in 1
or 0 for each cell.
~Sort all rows on the 1/0 column. Shade either the 1 section or the 0
section.
~Sort all rows again on the numbered column 1 thru X.

Another user-friendly way:
install ASAP utilities. It is freeware. Contains over 300 useful and powerful utilities to fill the gaps in Excel, and automate frequently used tasks.

I installed recently and am very satisfied.
Still, it seems that it doesn't have UNDO. So, be careful.

link to download:
http://www.asap-utilities.com/

Hope you will find it useful!