Alright. So it's a built in laptop microphone. No problem, there are solutions for this.
If you're gaming through Steam, you can actually use Steam itself to set this up.
Just click "Steam" at the top of the "Steam" browser, then click "Settings" and "Voice."
THEN, click the "Change Device" button. Select "Microphone" and click "OK, I'm Finished Changing Settings."
AND THEN, click the "Test Microphone" button and make some noise. Adjust the sliders for the outgoing and incoming microphone volume to get the level of volume you prefer, moving the slider to the right makes the volume louder. Click "Stop Microphone Test" when you're done.
After the testing, you can set that push button feature you want. Click "Use a Push-to-Talk Key to Transmit Voice" to enable the microphone only while you are holding down the transmit key. The default is "v" I think, if you want to change it just click "Push-to-Talk Key" and press the key you want to use. Click "Ok" to exit the setup.
However! If you're not gaming through Steam, then there are other solutions.