Call waiting means that you receive notifications of new incoming calls during an ongoing call. You can activate this setting in the settings section of your Samsung Galaxy S7.
1. To activate call waiting on the Samsung Galaxy S7 open the "Phone App" from the home screen.
2. Touch "More" in the upper right corner of the screen, and then click "Settings" in the menu that opens.
3. In the next submenu, scroll down a bit until you see "More settings" as the menu item. Select the entry.
4. As a penultimate menu item you will see "Call waiting" in this menu. Activate the option now using the slider.
From now on if you receive a new call during an existing telephone call, this is indicated by the "Call waiting" sound. So you will not miss new incoming calls on your Samsung Galaxy S7anymore.