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What is Unity?

Unity is a game engine: a program that handles graphics, physics, sound and input so you can focus on making your game. You build scenes in the Unity Editor and add behavior with C# scripts.

The four building blocks

A LEGO set. A GameObject is a blank baseplate. Components are the bricks you snap onto it: wheels make it roll, a motor makes it move, a light makes it glow. A Scene is the table where you set up your creations, and your Assets are the box of spare parts.

Almost everything in Unity comes down to four ideas.

Concept	What it is	Real-world comparison
Scene	A level, menu or screen. It holds a list of GameObjects.	A stage in a theater
GameObject	Any "thing" in a scene: a player, a light, a camera, an empty folder object. By itself it does nothing.	An empty box
Component	A piece of functionality attached to a GameObject: a mesh to draw, a collider, a script.	The things you put in the box
Asset	A file in your project: models, textures, sounds, scripts, prefabs.	Props in the storage room

For example, a "Player" GameObject might have these components:

Transform: where it is, how it is rotated and how big it is (every GameObject has one)
Mesh Renderer: draws the 3D model
Capsule Collider: gives it a physical shape
Rigidbody: makes it fall with gravity and react to forces
PlayerController: your own C# script that reads input and moves it

A Scene holds GameObjects. Each GameObject is a container, and its behavior comes from the components inside it, including your own scripts (highlighted).

Key ideaUnity uses composition. Instead of writing one giant "Player" class, you combine small components. Want something to fall? Add a Rigidbody. Want it to make noise? Add an AudioSource.

The Editor windows

Window	What you use it for
Scene view	Move around the world and place objects.
Game view	See what the player sees through the camera. This is where the game runs when you press Play.
Hierarchy	A list of every GameObject in the open scene. Dragging one onto another makes it a child.
Inspector	Shows the components of the selected GameObject and lets you edit their values.
Project	Your files (assets). Like a file explorer for the `Assets` folder.
Console	Shows messages from `Debug.Log`, plus warnings and errors. Double-click an error to jump to the line of code.

Play Mode

Pressing the Play button runs your game inside the Editor.

Changes in Play Mode are lostAnything you change in the Inspector while the game is running goes back to how it was when you press Stop. This is on purpose, so you can experiment safely. If you find values you like, write them down or copy the component (right-click the component header > Copy Component), stop, then paste the values.

Units and directions

1 unit = 1 meter. Physics works best when objects are roughly real-world size. A human is about 2 units tall.
Y is up. X is right and Z is forward.
Unity uses a left-handed coordinate system. If you come from Blender (which uses Z-up), models may appear rotated.
Angles in the Inspector are in degrees. Some math functions (Mathf.Sin, Mathf.Cos) use radians. See Mathf.

2D vs 3D

Unity does both. A 2D game is still a 3D world viewed from the front with an orthographic camera. The main difference for scripting is that 2D physics uses separate components: Rigidbody2D, BoxCollider2D, and callbacks like OnCollisionEnter2D. 2D and 3D physics do not interact with each other.

Next step

Continue to Your First Script.

This page is a simplified, AI-assisted interpretation. For the complete and authoritative reference, see the official Unity documentation.