Web3d is like playing with dolls in a storybook but on the computer. Imagine your mommy reading you a fairy tale and as she reads it, you can see the characters and places in the story in 3D on the computer screen. This is what web3d is.
Just like how you can move around a doll in your hand and make it do things, you can move around these three-dimensional characters and scenes on the computer screen. This is all possible through certain special web technologies like WebGL and Three.js.
Web3d is useful for making cool things like games, educational websites, and even real-world applications like architectural planning. Overall, web3d allows you to experience things online in a more interactive and immersive way.