Here's the repo for learning typescript from this Bilibili course: 尚硅谷TypeScript教程（李立超老师TS新课）

Course Link: P3 02_TS的类型声明

// declear with type
let a: number;
let b: string;

// declear with type and value
let c: boolean = true;

// ts can auto detect 
let c = false; // here ts will know that c has to be boolean.

Compile typescript file:

tsc example.ts

notice that there are many ways to specify how we want to compile (to es3, es6, or others)

The types of typescript: