Please help me in creating developing environment ,I downloaded all the things which are mentioned in the readme file but I don't understand how I use them to make development environment
Do you want to create an extension development environment?
Yes , I want to make development environment for making contribution in MIT App Inventor.
If you're just looking to build an extension, the previous resources identified should be sufficient, but if you're looking to contribute to the App Inventor core, you'll need to be able to build the full system. The easiest way is to follow the Vagrant instructions, but performing a build via vagrant can be a bit slower than doing it natively on your machine. Consider following the slideshow linked in the readme if you need step by step instructions.