If your phone supports Android 7.1 Nougat or higher, you may have side-by-side apps by following the following instructions:
1. Press the square "Overview" button next to the home button.
2. Press and hold the title bar of an app and drag it to the top or left of your screen and it will open in a half window.
3. You can now use the other half of your screen to do other tasks, enable multi-tasking.