Typescript is a superset of JavaScript which allows you to statically type JavaScript code. This means that you declare the types of variables (integer, string, …). It allows for a better developer experience as the Typescript compiler can catch many errors ahead of time since it checks the types of the objects ahead of time. It also allows developers to tap into extra features on top of JavaScript which allows writing more expressive JavaScript. Remember that Typescript cannot be run by the browser and needs a compiler to convert TypeScript code into runnable JavaScript. Typescript is widely used by the web-development community thanks to its features that improve security, readability, allow for a better development experience inside of the IDE with autocompletion, and add cool new syntactic sugar on top of JavaScript.

I recommend going to the Typescript documentation, it is good to get into the habit of going to official documentation since they are usually the right place to visit if you are learning new technology. Once you have the basics down try building a simple application with it or refactor an existing application in a way that uses the technology that you are learning.