OK, welcome to Raymarine. ST=SeaTalk which all have round three tire twist on connectors
ST1=SeaTalk1, which all have crescent shaped three wire connectors. ST2=SeaTalk2 (I've never seen these) are 5 wire cables and I don't know what the connectors look like. Think you have ST or ST1
STng is SeaTalk next gen and is (almost) identical to NMEA 2000 (the connectors are different). STng can be converted to the old ST, ST1, and ST2 using (you guessed it) ST? to STng adapter plug.
The real question is what does the rest of your SeaTalk network look like? What device do you want to connect it to? The best way to understand this is to download the ST networking guide from the raymarine site. It has lots of pictures of the various things you can and cannot get away with.