How do I do a Windows-Left or Windows-Right on Apple? I want to have 2 windows next to each other using a shortcut. How do I do that?
On the top left The Green Button for full screen / maximize have three ways:
short click -> app goes to full screen, creates a new desktop
long click -> app goes half full screen and you can choose from open windows for another half for the screen (that's a new desktop workspace too practically)
option+click -> app goes "old style maximize"

If I get your question well, the "long click" is what you are looking for. Only works in El Capitan 10.11, this is new feature. For older versions there were plugins to emulate Aero snap