What model of iPhone do you have exactly? What iOS version is it running?
How you get Control Center depends on the model of iPhone.
iPhone 8 and earlier, swipe up from the bottom of the iPhone.
iPhone X and later, you need to swipe down from the top right corner of the screen close to the edge. If an app is open when you try this, you need to make sure the Control Center is allowed within apps in Settings->Control Center->Access Within Apps.
More details here: Use and customize Control Center on your iPhone, iPad, and iPod touch - Apple Support