API Level: API stands for Application Program Interface. This tells Android Studio which version of Android you'll be targeting and therefore defines who will be able to use your app and which features you need. The objective is to ensure you have the broadest audience possible, while supporting any of the more recent Android features you need for your project.
Hello World: The traditional first project a developer will make when learning a new programming language or using new tools is called 'Hello World'. This simply prints those words to the screen.
Package Name: The unique identifier for your app that will be used to distinguish it on the app store. This will consist of your app name + a domain that you may or may not own.