If you are new to Excel, you will use the Alignment tab quite often. Found on the Home Tab of the Ribbon (Excel 2007 version), the Alignment tab allows you to position (justify) text in a cell.
From Top left to right, Horizontal alignment of text (top of cell, centered, and lower. The bottom left to right left justify, center and right justify.
Other features of the alignment tab include indenting text, wrapping text in a cell and merging multiple cells (basically creating one large cell). You can even change the text direction from the Alignment tab.
Clicking on the lower right hand corner of the tab will bring up the Format Cells dialog window to even give you more formatting options.