Nothing much to say about this lab. Just follow the instructions very carefully.
On page 3-12 there is a parenthetic remark about clicking on the OK button after creating the OR function and thereby prematurely terminating the creation of the IF.
The solution is: do not click on the OK button when you finish a function nested inside another function. Instead just move the mouse up to the formula bar and position it in the middle of the name of the function that you want to resume building, the IF in this case (literally position the cursor between the I and F of the word IF), and click the mouse. The function argument dialog box for IF returns. Now move the mouse into the field you want to resume working on and click. This activates the dialog box again. Only when everything is finished do you click the OK button.