First of all you should understand what TypeScript is.
TypeScript vs. JavaScript – Hacker Noon[
^] gives a good explanation.
You could also search with Google for e.g. Typescript vs Javascript.
TypeScript is a superset of Javascript which is strongly typed as the name TypeScript suggests.
A web browser does not know about TypeScript and can only understand JavaScript.
When deploying TypeScript is transpiled to JavaScript.
Angular apps itself can also be developed with only JavaScript.
But it is recommended to use TypeScript as the tutorials show.