When someone calls you, you'll see an incoming call screen with the option to accept or decline, along with a ringtone that repeats until you respond.
Once a call is connected, you can minimize it to a small floating bar that stays visible while you browse the rest of Chillverse — so you can keep chatting, checking your profile, or doing other things without needing to stay on the call screen the entire time. Tapping the minimized bar brings you right back to the full call screen, and you can end the call from either view.