Every writing software will have some form of spellcheck. This is a boon and a bane. We often rely on it too much. Don’t get me wrong, it is a massive time-saver. All those red and blue squiggly lines quickly highlight spelling and grammar to correct. But spellcheck is not infallible.
It is the first thing you should check when you finish but it is not the last thing you should do.
By all means, put your cursor at the top of your document and ask spellcheck to go over it. The software will quickly catch most of your errors, as well as double spacings, errant commas and full stops. It is fantastic.
However, sometimes your spelling is okay but the phrasing is off.
Example. The cat sat at the mat. Spellcheck was fine with that.
If you are using acronyms or product names that the software doesn’t recognise, be wary.