Autocorrect in OS X is a polarising feature; some users love it, while others abhor it. One of the reasons it is so disliked is it’s uncanny ability to mess up, often turning a small and innocuous spelling mistake (or brand name) into something entirely different, rendering what you have written completely incomprehensible.
Another common cause of frustration is the suggestion feature, which forces you to stop typing and click the tiny X to dismiss it. Recently after searching online for an answer to this I discovered many sites incorrectly stating that the Escape key dismisses the suggestions. While this may have worked prior to El Capitan, it certainly is no longer the case.
You will be pleased to know however, that it is still possible to dismiss and even choose from multiple suggestions by simply using your arrow keys, see below:
If you still would rather not use autocorrect take a look at: How to Disable Automatic Spelling Correction in Mail and Safari