You can download the Teamspeak 3 client from here:
It is available for Windows, Mac OS X and Linux. If you are running a 64 bit operating system then make sure that you download the 64 bit version of Teamspeak 3.
You can connect to it at the following address:
You do not need to sign up for a myTeamspeak account although it won't hurt if you do.
You do not need to install Overwolf but it won't hurt if you do. If you are regularly using voice communications in-game then it maybe extremely useful as it will show you who is talking at any given time.