How to enable push to talk in Steam

If you are using a microphone, or a gaming headset when you play on Steam, then the default setting for chatting with your friends is Open Microphone. It means your microphone is enabled all the time while you are playing. If you want to change it, just follow the following simple steps.

Open Steam and log in.
Go to the Friends menu at the bottom right corner of the Steam main window, your friends' list will open.
Click on the Settings gear icon at the top right corner of the friends' list, and a new window will open.
On the left panel of the friends' list settings menu, go to Voice.
On the right panel, scroll down to Voice Transmission Type and select Push To Talk.
Just below Push To Talk, you can see a field named Push to talk hotkey assigned as, and a button just next to it, click on that button to assign the push-to-talk hotkey.
Type the key you want, and it will be assigned as the push-to-talk action.
Close the menu.