Before we go further, you should know that the trsnic is still very in development, and it isn’t a simple plug-and-play solution. There are other options on the market to add connectivity, but they tend to be either expensive or lack performance. This is a more capable and affordable option, but it will take some significant experience to use.
Cetinski built the trsnic around Arno Puder’s RetroStoreCard, which utilizes an ESP32 development board as a network intermediary. The trsnic code runs on the RetroStoreCard — for now — and works in the same way, with the ESP32 bringing TCP/IP to the TRS-80. That, in turn, opens up possibilities for HTTP and FTP network protocols that are necessary for modern internet-based connections.
If you want a trsnic to use with your TRS-80, you’ll need to build it yourself for now. The files are all open source, so you can get a PCB made and assemble it yourself. Cetinski also plans to sell pre-assembled boards, and will continue development to make trsnic easier to use.