How to turn the iPhone on again?

I need urgent help! I have an iPhone 8 and just wanted to turn it off because I couldn't use WhatsApp. When I wanted to turn it on again there was suddenly a black background with a laptop and charging cable on it, what should I do?

Please hold down the power button and the home button until the screen goes black. Either the device then starts by itself, otherwise, please press the power button again until the apple logo appears.
Then does the device start?

Charge mobile phone?

Unfortunately it didn't work but thanks for the tip.

Thanks for the tip my cell phone came back on