The most valuable thing you can have in front of you when taking instruction from air traffic control is a piece of paper (or a notebook) and a pencil or pen. You can then write down instructions as they are read to you, repeat them back, and have them for future reference.
If you want to listen to and talk to others in flight, you will need to join the VirtualFlight.Online Discord server. Discord is an application you can run alongside Microsoft Flight Simulator, and provides excellent live voice-chat and screen-sharing facilities for free. Discord server membership is by invitation - visit bit.ly/virtualflightonlinediscord to get a free invite.
The ATC voice channel in Discord will enforce "push to talk" - meaning you must have a key or button mapped, which must be pushed down while talking. Push to talk results in only intended messages being communicated, and keeps the airwaves clear for other pilots.
In order for Air Traffic Control to see you on radar, you will need to run a small application called "Transmitter". Transmitter broadcasts your position in Microsoft Flight Simulator to a database online, which ATC can use to display your position within LittleNavMap. Within the Transmitter application you can set the callsign you will be seen as by ATC.
Within Discord, it is helpful if you change your username to reflect your callsign (so ATC know who is talking) - to do this:
Click on the Server Name at the top left of Discord
Click on "Edit Server Profile"
Change your display name for the VirtualFlight.Online discord server
As an example, Jonathan's callsign in Transmitter is "G-JBEK", and his username in Discord is "G-JBEK Jonathan".
Read the page on callsigns to help choose one!