I want to start with NativeScript, But when I went to see official NativeScript docs to getting started https://docs.nativescript.org/#get-started this show me two option for getting started.
Which one should I use? What is the difference between these two?
The difference is the second option uses Angular (2+), so if you like that then go with that. If your app has many screens it may be easier for you to use Angular, but if it's something you need to create quickly without too many screens then you can go with 1 as well.
Note that with option 1 you can also use TypeScript. It really pays off to learn TS no matter which option (with or without Angular) you prefer.
If you go the Angular route I'd advise you to first take the Tour of Heroes tutorial at https://angular.io/docs/ts/latest/tutorial/