Unable to speak on frequency?

I’m pretty new to Vatsim, and succeed to connect to the network. I flies Cessna 172. I didn’t find any way to talk/speak on freq, but I can hear others and i can just texting. Which really confused me. Is there a way to speak on freq, like pressing which button on keyborad(because i don’t have a yoke)? Thank you.

the documentation for the pilot client you are using will have an explanation on how to set up a PTT

thanks for replying! i’ll take a look