docs: update documentation for plotfig usage

Updated the Chinese and English documentation for the single_group.md file with:
- Corrected section heading from '多子图' to '多坐标系'
- Improved clarity and consistency in explanations
- Fixed formatting issues in code blocks and markdown structure
- Updated example content to reflect current API usage
- Maintained consistent terminology across both language versions

Author: RicardoRyn

docs/en/index.md

@@ -24,7 +24,45 @@ The project adopts a modular design, containing the following main functional mo
 
 ---
 
+## Core Three Elements of Matplotlib: Figure, Axes, and Subplot
+
 Fun fact: All elements of a figure[^1].
+
 ![Parts of a Figure](https://matplotlib.org/stable/_images/anatomy.png)
 
+When using Matplotlib to create plots, Figure, Axes, and Subplot are the three most fundamental and essential concepts.
+Understanding the relationship among them is key to mastering Matplotlib's underlying logic.
+
+### Figure (Canvas / Graphic Window)
+
+A Figure is the top‑level container for the entire plotting.
+You can think of it as a blank canvas or the graphic window that appears on your screen.
+The Figure holds all plotting elements.
+
+You can set global properties on it, such as the overall size (figsize), background color, resolution (dpi), etc.
+
+### Axes (Coordinate System / Plotting Area)
+
+Axes are the actual “plotting area” in Matplotlib, and where most of the data manipulation and drawing happens.
+An Axes is a rectangular region equipped with a data coordinate system.
+It includes not only the graphical elements you draw (lines, scatter points, bars, etc.) but also all auxiliary components such as the X‑axis, Y‑axis, tick labels, axis labels, titles, and more.
+
+A single Figure can contain multiple Axes objects.
+These Axes can be arranged in a regular grid, or they can be placed freely anywhere on the canvas, independent of any grid.
+
+### Subplot (Sub‑plot / Grid Partition)
+
+A Subplot is a special term for an Axes that is placed in a regular grid.
+When you want to display multiple charts neatly on one canvas (for example, a vertical comparison or a 2×2 layout), you divide the canvas into a regular grid.
+Each grid cell then contains an Axes, and that Axes is called a Subplot.
+
+In essence, a Subplot is exactly the same as an Axes.
+They share the same properties and methods (both can be used for plotting and for setting axis properties).
+The only difference is that Subplots are created in batch using the subplots() function, which arranges them in a predefined grid.
+
+!!! info
+    Subplot: specifically refers to an Axes that is generated via subplots() or add_subplot() within a regular grid.
+
+    Axes: a broader concept. It includes not only grid‑based subplots, but also axes placed arbitrarily on the canvas using `add_axes([left, bottom, width, height])`, as well as embedded inset axes (Inset Axes) nested inside a main plot.
+
 [^1]: [Quick start guide of matplotlib.](https://matplotlib.org/stable/tutorials/introductory/usage.html#parts-of-a-figure)

docs/zh/index.md

@@ -24,7 +24,43 @@
 
 ---
 
+## Matplotlib 核心三要素：Figure、Axes 与 Subplot
+
 烫知识：一张图上的所有元素[^1]。
+
 ![Parts of a Figure](https://matplotlib.org/stable/_images/anatomy.png)
 
+在使用 Matplotlib 绘图时，Figure（画布）、Axes（坐标系） 和 Subplot（子图） 是三个最基础、最核心的概念。
+
+### Figure（画布/图形窗口）
+
+Figure 是整个绘图的最顶层容器。
+你可以把它理解为一张空白的画布，或者是电脑屏幕上弹出的那个图形窗口。
+Figure 承载着所有绘图元素。
+你可以在它上面设置整张图的尺寸（figsize）、背景颜色、分辨率（dpi）等全局属性。
+
+### Axes（坐标系/绘图区）
+
+Axes 是 Matplotlib 中真正的“画图区域”，也是绝大多数数据处理操作的发生地。
+Axes 是一个带有数据坐标系统的矩形区域。
+它不仅包含你绘制的折线、散点、柱状图等图形，还包含了 X 轴、Y 轴、刻度标签、轴标签、标题等所有辅助元素。
+
+一个 Figure（画布）上可以包含多个 Axes（坐标系）。
+这些坐标系可以按网格整齐排列，也可以脱离网格、在画布上任意浮动。
+
+### Subplot（子图/网格分区）
+
+Subplot 是 Axes（坐标系）在网格排列下的一种特殊称呼。
+当你想在一张画布上整齐地展示多张图表时（比如上下对比，或 2x2 的四方格），就需要将画布划分为规则的网格。
+划分后，每一个格子里的坐标系，就叫做 Subplot（子图）。
+
+Subplot 本质上就是一个 Axes。
+它们具有完全相同的属性和方法（都可以画图、设置坐标轴）。
+唯一的不同在于，Subplot 是通过 `subplots()` 函数在预设网格中批量生成的。
+
+!!! info
+    Subplot（子图）：专指通过 subplots() 或 add_subplot() 在规则网格中生成的 Axes。
+
+    Axes（坐标系）：是更广义的概念。它不仅包含网格里的子图，还包含通过 `add_axes([left, bottom, width, height])` 方法在画布上任意位置浮动的坐标系，也包含嵌入在主图中的嵌套小图（Inset Axes）。
+
 [^1]: [Quick start guide of matplotlib.](https://matplotlib.org/stable/tutorials/introductory/usage.html#parts-of-a-figure)