First make sure both computers are on the same network. WiFi will work, Ethernet is better (no you can’t just plug in a regular ethernet cable between 2 computers). You need to have a router in between them that hands out IP Addresses.
The Live Link button is in the upper left hand corner.
For Windows computers, if they are on the same network, and the Link button isn’t showing up, you may need to setup your audio drivers. In your audio preferences, your driver type will probably say something like MME/DirectX. This driver won’t work with Link.
The reason this won’t work is that you need lower latency in order for 2 computers to sync their clock. If your computer takes too long to generate sound, the other computer can’t calculate the sync time, thus the link button won’t show up.
To fix this, download and install ASIO drivers. If you are using your computer’s internal sound card, download the latest version of ASIO4ALL at www.asio4all.org
If you have an external interface such as a USB Audio interface. Google ASIO drivers for your interface model and download from the manufacturer’s site.
Mac users should be using the native Core Audio driver.