Good question!
Yeah, it's easy for some of us veterans to forget that we were once very new to this game too :-)
Now, a very important detail here is the Minecraft version you're playing. Are you using the so called Java edition or the Bedrock edition? I only know the Java edition myself, so I'll be focusing on that.
A Minecraft server is basically nothing more but a Minecraft game which allows more than one player to connect to it. If you play a single player world try hitting pause, and then click on "Open to LAN"; now you're actually starting your own (mini) server which will allow other players to connect to it (as long as they're on the same network as you, it's a long story).
Now, if you check the
server section of Planet Minecraft then you'll find a list containing
thousands of different servers, 6821 at the time of writing. My suggest would be to skip over the list and check for anything you'd like. Many servers have a specific 'theme' to them. For example: survival servers focus more on the actual game of Minecraft, PvP servers focus more on fighting, so called "minigame servers" usually provide many games which you can play inside the game of Minecraft.
So how to connect?Every server entry will show a section called "
Connect with". That will be the name you need to connect to that server. Sometimes it's just a name, and sometimes it also has a number behind it; if so you need to copy the entire name (including the number).
Connecting is easy. Start Minecraft and click on the Multiplayer button. Now you have 2 options.
If you just want to check a server to see if its anything you may like you could use the "Direct connect" option at the bottom. Click on it, paste in the name which you got behind that "
Connect with" section I mentioned earlier and then click "Join server".
When you found a server where you want to play more then you should consider adding it to your server list. It's easy: Instead of clicking "direct connect" click on "Add server". Enter the name you want to give it, and then the so called server address (which you use to connect). Click done and you should be ready.
Eventually it could look something like this:

Ignore the two servers in the middle; those are my personal (private) servers, not publically available to other players, but the first and last in this list are public servers and happen to be two of my personal favorites.
And there you have it.
Oh, that Spigot part? Ignore that. Spigot is merely a type of Minecraft server which allows the server operator to use plugins which can enhance the game a bit. But as a player this is really not very interesting, just focus on finding a fun server and ignore the technical stuff.
Hope this can help you!