For clarification, an Amazon Firestick enables you watch films, (they are FILMS imo, NOT "movies"), programmes on catch up etc on your tv, regardless if it isn't a "smart" tv.
The Amazon Fire is a tablet. You can use it to read books (Kindle) play games, use social media, send/receive emails, download apps to play games, take photos and much more.
Depending on the model you choose, it can also be voice activated, like the "Alexa" echo, dot etc. So you can ask questions like "who directed Gladiator?" and get a spoken reply.
You can also download and watch films and programmes.
It can create shopping lists, "to do" lists, set reminders, (for appointments etc) timers (handy when cooking!) And all sorts of other stuff.
Technical support is good, and prices won't make your eyes water.
There are often deals, and as mentioned, Black Friday deals will be available in November.
HTH.