I doubt this will be a good answer, but I'll give it a shot :)

TypeScript is just JavaScript but with a type system – a tool that understands how data is shaped and how it flows through your program. The type system lets JavaScript programmers take advantage of advanced editor features and tools like code completion and to prevent bugs that even experienced JavaScript programmers make frequently. TypeScript’s type system is one of the most advanced type systems in significant use, and in many ways eclipses the capabilities of languages like C# and Java while being highly expressive, easier to use, and a much better fit for JavaScript.

TypeScript makes it easier to write correct, bug-free code. For example, it will warn you as you’re writing your code if you call a function with a string instead of a number, access a non-existent property on an object, or if some variable might be null or undefined.

TypeScript also makes it drastically easier to develop large code bases because the type system ensures everything in the program remains consistent. For example, if you want to rename a method of a class, you can just do it and every usage of that method gets updated with the new name.

Depending on the novice, at this point I might go on to describe how one works with types in TypeScript (short answer: type inference, type annotations in jsdoc comments and/or using type annotation syntax), but maybe the above is sufficient. Let me know if you have more questions!