To start working with basic shapes in Fabric.js, you first need to create a Fabric canvas using the fabric.Canvas constructor and link it to your HTML <canvas> element. Fabric.js provides built-in classes for common shapes like Rect, Circle, and Triangle. Each of these objects is created by calling its constructor with a set of options that define its appearance and position.

For example, when you create a rectangle with new fabric.Rect, you can specify properties such as left and top (for position), width and height (for size), and fill (for color). Circles use a radius property instead of width and height, and triangles have both width and height like rectangles. You can also add outlines with the stroke and strokeWidth options.

Once you have created your shape objects, you add them to the canvas using the add method. You can chain methods or set properties directly on each object to customize them further. This modular approach makes it easy to build complex scenes by combining and configuring different shapes.

Object options let you control many aspects of each shape, such as transparency (opacity), rotation (angle), and whether the object can be selected or moved. You can combine options for even more customization, and you can chain methods to update properties after creation if you want to change how a shape looks or behaves.