If you regularly use Apple Mail, Word, or some other application where you do a lot of writing, macOS Sierra comes with a few new options: auto-capitalization and auto-periods. You just have to manually enable them.
These options already exist in iOS, so if you use an iPhone or iPad, you already be acquainted with auto-capitalization and auto-periods.
To enable auto-capitalization and auto-periods in macOS Sierra, first open the System Preferences and click “Keyboard”.
In the keyboard preferences, click the “Text” tab. In the upper-right corner, you will see the two options, “capitalize words automatically” and “add period with double-space”. Check either or both options if you want to enable them.
Auto-capitalization is easy enough to understand. It means that at the beginning of every sentence, or whenever you use a proper noun, macOS will automatically capitalize that word. The auto-period feature means that every time you double-space at the end of a sentence, macOS will insert a period.
These options are off by default since most people can handle capitalization and periods themselves. But if you want to ensure that your Mac is looking out for you, then you may like to have them on.