Many of us have the habit of keying in the same wrong word as we type, for example enter “don;t” when meant “don’t”, or key in “teh” for when we want “the”. Here a quick tip that makes use of OS X’s text replacement feature to make your Mac automatically correct your spelling mistakes as you type.
Go to System Preferences > Keyboard and select the Text tab. Click on the (+) to add entry. For each entry, type the text to replace (such as “don;t”) in the Replace column, and its replacement (such as “don’t”) in the With column. Once setup, text that you type in most OS X edit window that matches the entries will be automatically replaced.