This page provides tips on selecting cells individually and in groups.
Excel acts on cells you have selected.
If you begin typing, you'll start entering information into the currently selected cell, even if there's already something in it. Use the Big Fat White Plus Sign when selecting, or you might wreck your spreadsheet:
Hover the Big
Fat White Plus Sign over the cell you want
to select, and click once on the left mouse button. Until you become
accustomed to the screen, check the formula bar to make sure you've selected
what you thought you did. You'll get used to it after a while, and
won't have to check any more.
The entire area will be shaded in, except the cell that's currently active. That cell will still look normal. It's the one you would type over if you begin typing now.
(While you're selecting, Excel will momentarily show you how many rows and columns you've selected, as in the 9R x4C above. When you stop, it will show you the currently selected cell address (A1) again.)
Hover your Big
Fat White Plus Sign over the title letter
of the column and click once on the left mouse button.
Hover
your Big Fat White Plus Sign over
the title row number (all the way on the left), and click once. The
title row number and the line will be highlighted.