Split screen

You can use the App Switcher, see this Apple article: 

See the following Apple articles:

Switch between open apps on iPhone

Switch between open apps on iPhone – Apple Support (UK)

Switch apps on your iPhone, iPad or iPod touch

Switch apps on your iPhone, iPad or iPod touch – Apple Support (UK)

It is possible, but you need 3rd party app, search at the App Store.

Split View is not a supported feature in iOS - iPhone.

Currently native Split View is only available on iPad.

Use multitasking on your iPad - Apple Support