You have made your sheet, with all kinds of complex formulae and logics.

Now you want to just take a run-through on all formulae that you made. What you do is select each cell where you have entered the formula and press F2 to go into the editing mode. Now you can see your formula. You do this for each of your cells. Painful, isn’t it!
 
Simpler way.
Just press Ctrl+~ (~ is next to the number 1 on your keyboard).
You now see all formulae present in all cells in the sheet, instead of the results of those formulae.
Review all the formulae and press Ctrl+~ to come back to the same way as before, where you see the results of the formule.
Thus use Ctrl+~ to toggle between the 2 views.
Keep Excel-ing through Excel!