To download D5 for Cinema 4D and start using features like LiveSync you'll first need to install the
D5 Launcher.
The launcher acts as a hub to manage projects and downloads, with news for events, webinars and updates. But the bit we're focusing on is found in Workflow on the left and then Sync. You can also find the other software D5 can connect to.
If you have not already installed the main D5 render you will need to download and install that as well. The order does not matter but you will need it before you can use D5 in C4D.
Once installed go into C4D and to Extensions to find D5 Sync to open the real time rendering window as well as a floating tool bar with your D5 controls. Continuing editing in Cinema4D and watch it be rendered in real-time in the other window.