This Go code is about creating a simple note-taking application. Imagine you have a digital notebook where you can write notes. This code sets up a system that lets you:

1. Add new notes
2. See all your notes
3. Change existing notes
4. Delete notes you don't want anymore

The program does this by creating a website (we call it an API) that other programs can talk to. It's like setting up a special phone line for your digital notebook.

Here's how you might think about writing this code:

1. First, you decide what a note looks like. In this case, a note has a title, a description, and the time it was created.

2. Then, you create a place to store all the notes. Here, they're just keeping them in the computer's memory (like a temporary notebook).

3. Next, you set up different ways to handle requests:

   • When someone wants to add a note, you take their information, give the note a special number (ID), and store it.
   • When someone wants to see all notes, you gather them all and show them.
   • When someone wants to change a note, you find the right note using its ID and update it.
   • When someone wants to delete a note, you find it by its ID and remove it.

4. Finally, you set up the "phone lines" (routes) that tell the program which action to take based on what kind of request comes in.

The code uses some special tools (like "mux" for routing requests and "json" for speaking a language that other programs understand) to make all of this work smoothly.

In essence, it's like creating a simple digital notepad that can be accessed and modified through a computer network, rather than directly on your device.