Samba TV began life creating apps for TV manufacturers. It worked with nearly every smart TV manufacturer - other than, notably, Samsung - to create the basic apps and various OS infrastructure pieces that you see when you use a Smart TV. In other words, it made all the stuff that you ignore when you open Netflix, Hulu, or Amazon Prime on your smart TV. This isn't entirely relevant to their business anymore - but it gave them technical hooks into the operating systems of, and business relationships with nearly every TV manufacturer.
TV is an increasing challenge for advertisers. Content is often viewed on DVR, and when viewed on delay the ads may be skipped. Similarly for content producers, it's often unclear when content is viewed and to what extent. Manufacturing TVs is also an increasing challenge for the manufacturers. TVs are largely fungible, there is incredible margin pressure, and there is no revenue after the initial sale.
Samba approached these challenges in a relatively unique way - leveraging its relationships with TV manufacturers. They developed technology that grabbed a fingerprint of whatever was on the TV every couple seconds. This is then sent over the internet connection you set up to watch Netflix to Samba. On their servers, they have technology that maps this fingerprint to all their known TV shows and commercials - enabling them to understand what consumers are doing, what ads they're watching, etc. - including Netflix.
Collecting this data enables Samba to act as a significantly improved version of Nielsen - actually helping brands and content producers understand what content is being viewed and when. Nielsen generally uses these in-home boxes in roughly 20,000 households to understand what's being recorded according to different demographics. Theoretically, Samba can be significantly more accurate than Nielsen on the measurement side, though maybe not with the demographic precision.
Samba can take this technology further. Apparently when you set the TV up for wireless, it can actually see the other devices connected on the wifi. This means your phone, laptop, tablet, etc can somehow be identified by their systems. They then have an offering that allows brands to target second screens when individuals are watching shows - or individuals that have watched certain shows. I personally don't understand how this technically works.
I will note that the service is opt-in, meaning you choose to enable the service when you start your TV. Samba then shares a significant portion of their revenue with the TV manufacturers, which enables TVs to be sold cheaper and with more features. And you could always opt out.