This is a great training tool, and you have a lot of work in this. I have some feedback as a first-time user. These may seem like a lot of comments, but it means I think your idea is great and worth refining. I am pretty experienced with VBA and would be happy to help in any way that you need help.

The instructions on sheet "1" should make it clear that the user should be putting his formula in B19. Nothing happens if you put formulas in other cells. This is suggested by the text but not explicit. You might also want to lock all cells except B19 and protect the sheet.

#3 says, "fill up all the arguments by using values from A1:D1". It is not clear what you are trying to do there. Get the user put in junk arguments to force the pop-ups to explain what's wrong? This will be confusing for most new Excel users, because they will confuse A1:D1 with what the VLOOKUP is supposed to do.

It might be better to walk them step by step through building the formula, rather than have them put in a complete formula then diagnose it.

The first text box that pops up says, "The blue cell is what you need to look for here." I had to go through several steps before I figured out what this meant. I don't think that is very clear. Maybe, "Your VLOOKUP formula will search for the value in the blue cell (A19)."

I suggest putting the "OK" button directly into the text box, rather than making it a separate window.

Column L, the double-head arrow from L3:O3, and the arrow from the text box to L3 all use the same green color which makes it a little difficult to distinguish what's going on, especially the arrow head from the text box. Think about using different colors or different shades for each distinct idea.

Text box describing third argument: Make clear that the leftmost column, where the value is sought, is counted as column 1 in this range. (It is a common error to think, "I need to move three columns to the right for my answer, so this number is 3.)

Sometimes when I enter a formula in B19, the blue arrow automatically comes up from the bottom and points to A18 but then stops. I have to press the "Show Guide Again" button to continue.

Suggest "Like what I mentioned" => "As I mentioned"