Windows 10 has the ability to auto-correct or highlight misspelt words in many applications, which is really useful when typing messages on forums like this one. This feature is enabled by default, but it can cause some problems when it tries to auto-correct words that are appropriately used by not in the dictionary (for example, unusual technical terms or colloquialisms). Unless you proof read what you have already written, you may not notice these auto-corrected words slipping through.
If you'd like to change the options for highlighting or auto-correction, click the Start Button followed by Settings:
Now select Devices:
Now select Typing from the left column and take a look at the toggle switches listed under Spelling. You can enable or disable auto-correct and highlighting of misspelt words by clicking the appropriate options: