How do I open the control center

According to Access Control Center on your iPhone and iPod touch - Apple Support:

• To open Control Center, swipe up from the bottom edge of any screen. 
• To close Control Center, tap the top of the screen or press the Home button.

To open Control Center on iPhone 8 or earlier:

Swipe up from the bottom of the screen

Swipe down or click the arrow at the top to close

iPhone X or newer:

Swipe down from the top right part of the screen

Swipe up to close

Hope it helps, Nikola