with the "call waiting" function, during an active telephone conversation, one is alerted that a second caller is trying to call. if "call waiting" is activated, a knocking sound is heard to draw attention to the second caller. the user can decide whether to accept the call (the first caller is put on hold) or reject it. if "call waiting" is deactivated, the second caller is automatically rejected.

Android 10 (One UI 2.0)
Step 1:  Open the  Phone App
Step 2:  Open the  Menu
Step 3:  Tap on  Settings
Step 4:  Tap on  Supplementary services
Step 5:  Enable or disable  Call Waiting
  1. Open the Phone App
  2. Open the Menu
  3. Tap on Settings
  4. Tap on Supplementary services
  5. Enable or disable Call Waiting

Samsung Instructions