He means that using the browser add-on you canroute nly browser traffic via VPN, but nothing else
(example: games, chat apps, etc)

Some nodes are not working because of different reasons, mostly because Linux skills are required with this beta version and some people tries it anyway without knowing how Linux works. Also the guides how to setup the nodes needs a bit of improvement. I have written my own guide as text file which is available in Lethean discord message board. But we have a node rating system so if you choose exit nodes with high rating your chances to get a working node is higher. You can try the Lethernet nodes. I am the operator the Lethernet nodes and tries my very best to keep them working. At the moment there is only web browsing proxy mode. VPN will come later. According to roadmap 2019 Q1.

When the payment is done you have to wait around one minute for the payment to arrive to the node. You can see this in wallet when onlime timer starts to count you have got a connection. Then you must have Lethean Browser Extension installed in the browser. Currently Chrome is supported and Firefox version is coming soon. You press connect in the browser extension. Now you can confirm by visiting checkmyip.com that your location have changed.

As an experiment I have added DNS based adblocking in one of my nodes (in Amsterdam). I probably will add it in other nodes too but not all of them. It works quite good even if it not remove all ads to 100%. As example some ads are served from same address as the content (like Youtube video ads) but it  remove most of the ads. I have other nodes without this adblock so you can choose if you want it or not by selecting the node that you like most. And you can also try other node providers. I have seen a few working nodes on locations that I not provide yet. Go by the rating.