OS X El Capitan auto-correction crazy
If you want to turn it off, go to System Preferences &gt; Keyboard &gt; Text (tab)  and unselect auto-correction.
If you want to do more, then on the same page you can tell it what language to auto-correct (if you don't want it for all languages you use on your Mac) or specific words (on the right you click the &quot;+&quot; to add specific auto-corrections.
If you want to disable auto-correction of a single word, then look at this answer already given:
Answer already given for &quot;Can I disable auto-correction of a single word on OS X&quot;