The most basic way to view discord is as a place to talk to other people, either directly or in groups.
For example, what is a server? Is your server different than your account, or is it part of it?
A server is a community of people who are all there to talk, usually about a particular theme. For example, the Stardew Valley server is a community for discussing the game, and related topics like game modding and fan art. Most servers also have spots for off topic discussion.
Much like these forums, servers will be divided into "channels" which usually have a specific topic. Each channel is a place for people to send messages, which display in real time.
How can I find a certain community on there, or is that even possible?
If you're using Discord as a desktop app or in your web browser, there is a button in the bottom left labelled "Explore Public Servers". In this section you can search for servers to join, but be aware that this does not display all servers, only ones that have a large number of people on them and have opted into being listed there. You can also find servers through sites like
https://disboard.org/ or just by searching online.
How do you talk with people?
Once you've joined a server, you can send messages in channels, but you can also add people on Discord as a friend and message them directly. In the forum's LFG section, people will often include their Discord ID. You can use this ID to send them a friend request and talk to them directly.
I hope that answers the questions you had! I can certainly answer more if you have them. It sounds like you may have joined the Stardew server at this point, and you can of course ask questions there as well.