I think some very important points (not gameplay-wise, but learning-wise) are missing here.
(Note:This section is especially focused on zerk-gameplay, as roaming and smallscale are kind of a thing you need to learn/gather expierience by yourself)
1. If you see a commander on the map, try joining their squad. If it is open, it is usually a public lead (or the commander forgot to close the squad) that usually sits in some kind of voice-chat with an organized Zerk.
2. in any case: just should ask if there is a public lead, and if there is one: where they organize. like i said in 1., there is surely a TeamSpeak/Discord etc where the server community is organizing.
3. (maybe one of the most important points): if you don´t understand the calls of the commander: ASK what that means. Commanders usually don´t assume to have new players. But, from my expierience, if you tell the commander that you are new, they usually will adapt their lead a bit, explain a lot more than usual and take that into account (for example, that you perhaps don´t have war gliding, or the warclaw unlocked).
4. look for WvW-builds for your class, and make sure that you at least understand what your "task" is with that respective class. WvW differs heavily from PvE/sPvP in terms of builds and gameplay. You can usually get them from the bigger guilds on your server. Also, like said above, you may want to adapt your gear more towards defense to begin with, because dying in a fight does more harm to your teammates than dealing too low damage.
5. If you think you are getting a bit into it and have fun: consider joining a WvW-Guild. Don´t be too afraid, because some guilds have a very progressive style, there are lots of guilds out there, some looking for progressive, expierienced players, and some that welcome every new player and teach them even the basics of basics. This is imo the best way to learn about WvW
6. Don´t throw siege by yourself. The commander can see the amount of supplies inside of his squad, and he will calculate with that amount. Random people throwing siege can screw that up if people build up siege that hasn´t been placed by the commander, screwing up the calculation of his available resources.