Roku is basically the hardware. You get one, sign up for the account, and you can add thousands of channels, most of which you won;t want. The two main entities on the Roku box will be Hulu and Netflix. Both pay software. I have them both and love them, although they are not live TV, and you cannot get all the shows you normally get with cable. You can also add some stand alone networks, and some that will activate off your D.TV. I love my Roku box because the image quality is about 10 times better than cable. WHY? You may ask. Because cable jams phone, internet and 300 channels into one wire. The signal is so compressed it looks like shit. My Roku box shows HD so fucking clear I can count the pores in people's skin.
Fire TV pretty good, but if you really want the good stuff you need a Prime account from amazon. $100.00 a year gets the account and includes a lot of shit. I have an account. I also have a firestick, but find that the Roku is a much better option. The firestick has "okay" video quality. If it ever pukes on me I will get the box instead. If you get either box, there are various qualities you can choose. Get a quad core processor and about 4 to 8 gigs of ram for best quality and speed. Oh, and they both require a wifi net in the house.
I've also jailbroken my firestick and installed Kodi. BUT, most of the kodi repositories are down now so it's not much good. It MAY be good again. Time will tell.