1) Building a separate native android and iOS app not only increase time but cost also, that’s why companies ask for multi-platform app development and that’s where flutter comes into the picture.
2) Flutter is a mobile app sdk for building high quality app from a single codebase that means write once and use on both the platform android and iOS.
3) It comes with a host of libraries which helps to maintain native look of an app that means android and iOS app will continue to have their own native look.
Flutter use dart language so first and foremost need to learn dart. Well dart is pretty easy language to learn if you already know either of Java, Javascript, C++ or C# language it will take just few hours to get started, even same for the developer who have never coded in dart.
Here is dart editor to practice
(Dart for practice)[https://dartpad.dartlang.org/]
After that download flutter sdk and set the environment variable to that. Here steps needed is mentioned clearly
(Download flutter)[https://flutter.io/get-started/install/]
Visual studio code, android studio or Intellij Idea have flutter and dart plugin. Just add those plugin and you are ready to go.