Interactive TVs and whiteboards are, as you might have guessed, essentially interactive screens that let you easily navigate and manipulate your lessons as you present them. They come in two general varieties: large flatscreen TVs and whiteboards with an attached projector that (according to the manufacturers) can serve double duty as a more traditional whiteboard that works with dry erase markers when the projector isn't on. Both types generally offer touch functionality — some can support up to 16 simultaneous touch inputs to allow for maximum collaboration — and respond to both finger touch and special multi-functional styli that come with higher-end models.
The two major players in the market, SMART Technologies and Promethean, bundle proprietary software with their interactive whiteboards and TVs that enable teachers to create presentations, quizzes, polls, and interactive problems, projects, and other activities. On top of that, both companies provide extensive databases of lesson materials, including animated graphics, images, and other free assets that can be added to your own lesson plans. Promethean's ClassFlow Marketplace even offers full lessons that can be purchased individually.
Because these are web-based applications, you can build lesson plans on your home computer before you get to class, making it easy to take these materials for a spin before you debut them for your students. More importantly, this also means that students can access and interact with lesson materials using virtually any web-enabled computer or smart device.
If you want a more detailed overview, this video is a bit dated (not to mention lengthy) but gives a good gist of what these boards look like in action, while also spelling out some of the differences between SMART's and Promethean's basic offerings.