Download the To-Gather client here. That is the software to visit the 3D environment.
Choose "Autoconfigure" when connecting.
When you have installed the program you can log in as a Tourist, the e-mail address you fill in there won't be published.
You can walk through the worlds with the arrow keys. You can also use "w/a/s/d" keys instead of the arrow keys and use your mouse to look around, to enable this option press F2. For more help you can look in the users guide.
After the program has started you will automatically enter the world “To-Gather; the European House”, from there you can start exploring and continue learning.