The cell borders are highlighted, or if a range of cells are selected, the active cell will be a different colour than the others, usually being white. The name of the active cell will always appear in the name box.
The cell will be highlighted on the spreadsheet and will have a border box around it. If you have more than one cell selected, the selected ones will be a different colour. On the formula bar, just...
The cell is highlighted. The cell usually contains the cursor insertion symbol (I-beam). The cell reference is in the cell address box (top left corner, to the left of the formula bar).