I bet you all have played a Minecraft server, if it isnt obvious yet. Now, to connect to a Minecraft "server", you need to use the Server Address A.K.A the IP Address with Port. Now what is a server, and how are you joining it even thought its not in your pc, and you can connect with other people/friends? That is what we are gonna learn (I cant believe Im doing this).
As you have doubted, this server is not on your computer. But on someone else's! Yes, so you are connecting to another computer and playing Minecraft which is running there.
So, since you are connecting to another person's computer, you are using the Internet for it. And for each Wi-Fi router, there is one address, a kind of numbers like 123.432.12.123, just like your house does. Now ports, think of a port like a special door for your Minecraft server. Minecraft servers usually use port 25565 (unless specified (IP + Port = 123.432.12.123:25563)). When you connect to a server, your game knocks on this door (port). The server opens the door and lets you in!
A Port is opened in a person's computer, so that "you" can access it. But, there is a different way to this, called Port forwarding, we will look into this later.
You have probably seen that the IP address you type is (almost) always text, rather than numbers. Well, look I am right, but this is different. The TBC