Pubspec.yaml what this file does in Flutter

version: 1.0.0+1

The version of your application or package.

environment:  sdk: ">=2.0.0-dev.68.0 <3.0.0"

Your application or package claims to support Dart SDK within this version range

dependencies:  flutter:    sdk: flutter

Your application or package depends on the flutter package which can be found in the SDK

  sqflite: any

Your application or package depends on the package sqflite from https://pub.dartlang.org with no specific version constraint.

  path_provider: any  intl: ^0.15.7

Your application or package depends on the package intl from https://pub.dartlang.org on any version 0.15.7 or later but before 0.16.0.

  # The following adds the Cupertino Icons font to your application.  # Use with the CupertinoIcons class for iOS style icons.  cupertino_icons: ^0.1.2

The ^ changes the meaning for versions 1.0.0 and later.

^0.15.7 means >=0.15.7 <0.16.0^1.15.7 means >=1.15.7 <2.0.0

because for versions < 1.0.0 breaking changes are indicated by incrementing the middle number, while for >= 1.0.0 breaking changes are indicated by incrementing the first part of the version.

It is responsible for handling of importing images/fonts/third party packages which you want to include in your project.

As explained here on the Flutter site:

The pubspec file manages the assets and dependencies for a Flutter app.

More info can be found here.