Turn iPhone on or off

Press and hold Power button and volume button.

Screenshot

Press the Side button and the Volume up button at the same time.

Control Center

Airplane mode, WiFi, Bluetooth, Mobile data, brightness, volume control, flashlight, timer, or calculator – in Control Center.
to open – swipe down from the top-right edge

Change Wallpaper

touch and hold the Lock Screen

Custom Caller Image / Poster

Contacts app , tap your name, then tap Contact Photo & Poster.

Set up a mail account

Settings  > Mail > Accounts > Add Account.

Set up a contacts account

Settings  > Contacts > Accounts > Add Account.