Typically only offered to large YouTube channels with a wide audience (although not exclusively), another big way to earn cash through YouTube is to get sponsored deals with companies that will pay you to promote or mention their products in your videos. You can earn money this way either as a lump sum of cash the company will pay you for the deal, clicks on the company's link, or on a per-view basis.
But don't make the mistake of thinking this will be a passive source of income—you're on call whenever you have a guest and you'll always need to keep the place clean for incoming visitors. On top of just renting on Airbnb, consider offering your guests paid add-ons, like Lauren Gheysens', Royal Day Out in London, England—where she gives visitors a local's only tour of the city, complete with bespoke 18th century costumes.
When you're ready to add affiliate links to your website, the best place to start is with Amazon Associates, the number one affiliate network on the web. Once you sign up, you simply get a short link from the product page and embed it in your own website. If you're writing reviews, you should direct people to buy the product with your affiliate link. You can also try services like Clickbank, Avantlink and even eBay, which runs its own affiliate marketing program.
One of the cool things about Google AdSense is that it's so easy to get set up. If you have a blog or website, you can sign up for a free Google AdSense Account. From there, Google will give you a unique code that you will paste onto your website. Google takes it from there, tracking your page views, traffic, and earnings on your behalf. There is no upkeep or maintenance to get this thing going, which makes it a no-brainer if you have a website already.