Mac OS X El Capitan has introduced a new feature called Split Screen View which makes multitasking much easier by allowing you to open two apps side by side.
There are two methods you can use to employ the split screen view. Select your first app. Click and hold on the green Maximize button and drag the application to the right or left corner of your screen to pin it. Now, open the second app and pin it to the other half of your screen. The second method involves using the Mission Control to create a Split View Space. Do a three finger swipe to activate the Mission Control.
Drag your first app to the Spaces bar displayed at the top of your screen (over to the + button). Next, drag the second app window over to the first app. Mission Control will create a new split view space out of the selected app windows. Click on the combined apps to open them in a split screen view.
N.B. You can adjust the size of the app windows by moving the black vertical divider either left or right.