What is how to do split screen on mac?

Here's how to use Split View on macOS:

To enter Split View, you have a couple of options:

Using the Green Full-Screen Button: Hover your mouse over the green full-screen button in the top-left corner of a window. A menu will appear. Choose "Tile Window to Left of Screen" or "Tile Window to Right of Screen". This will move the selected window to fill half of the screen. After selecting the side you want to tile the window to, the Mission Control view appears. Click on any other window to set it to the other part of your screen.
From Mission Control: Open Mission Control by swiping up with three fingers on your trackpad, or pressing the Mission Control key (usually F3). Drag a window to the top edge of the screen where it says "Drag windows here to create a new Space." Create the space and then drag another window to that space.

Once in Split View:

Adjusting the Divider: You can adjust the size of the windows by clicking and dragging the vertical bar between them.
Exchanging Window Positions: Click and hold the title bar of a window, and then drag it to the other side of the screen to swap their positions.
Exiting Split View: Click the green full-screen button on either window to return it to full-screen mode. The other window will return to its previous size and position. Alternatively, move your cursor to the top of the screen to reveal the menu bar, and then click the green full-screen button.

Here are some related subjects that you may be interested in: