Hello there, Anthony!
1) Make sure you have set a push to talk keybind in Settings>Audio/Push to Talk (PTT) and with the keybind you assigned, you can use that to talk to ATC. If you already have assigned a keybind but you still can't transmit, check your audio settings in the section I showed you above.
2) You can tune into a frequency by typing .com1 (frequency). For example: .com1 118.100 or manually using your radio box.
3) Yes. If you are finished with your transmission, you can let your PTT key go.
If the problem persists, I'm happy to assist you more.
Have fu