Streaming

Hello Family,   I`m old school 76 I just don`t understand this streaming and dac business. I`m still stuck on my RTR`s, Cd player and  PASS lots of power.  It sounds very interesting.  I was once told that I could also do some serious taping using my RTR`s I`d would like someone to tell me what gear I would need and how to set it up forget my desk top or lap top.   I`ve heard terminology used like Innos zin mini, Bluesound Node, Aurender Are they streamers? what is Roon, Qobuz, Plex? whats the purpose of a dac? I`m on fixed income `what`s the best gear I can get for 1500 mostly buying used gear to began. Thanks