Automatic Fill in 2010

In an older version (I think 2003, maybe) I was able to highlight any cell I wanted to just by selecting the cell, meaning I wouldn't have to select the cell and then hit the fill button. I could "turn on" this function and in essence, any cell I put my cursor in would automatically highlight. How can I do this in 2010?

Thanks for the welcome!
Oh, I could see how this could be confusing when I'm using incorrect terminology. Not sure which is correct, but when I would click into a cell it would automatically turn the cell yellow.