How do I cancel the wavy line under the English letter in Word?

Here first ask a friend to open their own word, so that you can more intuitive understanding of why this wavy line

Here's an example for a friend. You can explain that there are some correct English words without the wave line, but some of them are not correct English words.

Here click on the red arrow here to show the sweet potatoes can be, see that "review", the leftmost has a lower triangular option

Select the first on the line, and then you can see the English words here to correct the hint, here can look at "options", the lower left corner

Eliminate the downward line, very simple, just click the right button, "Ignore All", click on it can be

Look here is already all the wave line just to kill, mainly want to let friends all-round understanding of why there are wavy lines