To split the screen into three on a Chromebook, follow these steps:
1. Hover over the Maximize button on the window you want to split.
2. In the menu that appears, select "Split" to divide the screen evenly.
3. Choose to place the window on either the right or left side.
4. Repeat the process with two other windows to achieve a three-way split.
5. To change the screen rotation, go to Settings > Device > Displays > Orientation or use the keyboard shortcut "Ctrl + Shift + Refresh."
In this way, you can easily split your Chromebook screen into three sections for multitasking.