You can see the tool in below which has two section Entered text and Corrected text. You have to write or copy your text in entered text section then just press the translate button.Now, you can see the corrected text in which wrong words are underlined.
You can also compare it by seeing corrected and entered text.And lastly make sure your text is not too long.
It is an tool/software which analyzes your text and check various possibilities of words that matches with your previous/next word and correct your text.It has huge amount backend that's why it could take some time according to length of text.
Grammar corrector is very useful in every aspect and has various reasons how can it would be useful.Some of those are
1. Of course it Saves time
2. Saves nerves
3. Since it tries many possibilities it has better feedback
4. It increased target audience
5. People are not well at english can practice here.