If you like the fact that when you type on your iPhone or iPad the first word of a sentence is automatically capitalised, and a full stop is added automatically after you press space twice, you will like these new options that arrived in Sierra.
Go to System Preferences > Keyboard > Text, and select: ‘Capitalize words automatically’, and ‘Add period with double-space’. (A period is a full stop, of course. This US term appears even if you have a British keyboard setup specified.)
Select these the two options by ticking in the boxes then the necessary capitals will be added in TextEdit, Pages, and similar apps automatically, while hitting space twice in a row will bring up a full stop and following space instead, just like in iOS.