To enter data into a worksheet, a cell must first be selected. A selected cell is outlined in black (or possible other colors). For example below, the cell A1 is selected and ready for data entry :
  If data is typed it can be entered into cell A1 only. Try entering your name in cell A1. Notice that your name also appears on the edit line. This is where data is edited if changes need to made. Remember, for information to be entered, you must follow the data with enter (), or an arrow key, or by clicking the mouse in another cell. Try editing your name. Select cell A1 and click the mouse on the edit line near the information you want to change. Use del or Backspace to delete items.

Numbers are entered in the same manner. A number will become a label (a non integer entry) if used in combination with letters. Try entering a number into cell B1.