The cells in a spreadsheet are quite small, so typing in a lot of information can lead to it overlapping and covering up other cells. One method for confining lots of information to just one cell block is text wrapping.
Try this out by typing a lot of text in to a cell so that is overlaps the edge. Next, select the cell by clicking on it, and then click on the Wrap text button in the ribbon above. After you have done this the text should be confined to the vertical cell borders, as seen below:
