C# in 60 seconds: variables

your project so far

Nothing to open yet. Unity first opens in lesson 05 — these first four lessons are pure C#.

A variable is a named box that holds one value. That is the whole idea.

animated diagram

Declare the box (type + name), then values go in and out of it while the game runs. The fourth box holds three numbers at once, and together they are a place on the floor.

The four types you actually need

the whole of C# basics, in 6 lines

int   hp     = 100;      // whole number 
float speed  = 5.5f;
bool  isDead = false;    // true / false 
string name  = "Knight";

Vector3 pos = new Vector3(0f, 0f, 0f); // a point in 3D

The type on the left tells C# how big the box is and what fits in it.
float always needs the f suffix — 5.5 alone is a double and will not compile.
Vector3 holds three floats at once: x, y, z. In Unity you use it constantly.
Naming: use lowerCamelCase for variables — that is the Unity convention.

Changing a value

C# script

hp = hp - 20;   // long form  
hp -= 20;
hp += 5;        // heal       
speed *= 2f;

Do this now

Nothing to open yet — just read the 6 lines above twice. The next lesson puts them inside a real Unity script.