You can share your app in an executable form (.apk) that can be installed on a phone, or in source code form (.aia) that can be loaded into App Inventor. You can also distribute your app on the Google Play Store.
Choose Projects > Save project from the top menu to save your app.
Choose Projects > My projects from the top menu to see a list of your projects. Select the project you wish to share by checking the box next to it.
Choose Projects > Export selected project (.aia) to my computer to export the source code for your project. The source code is downloaded in .aia file format.
You can now send the file to a friend and they can open it with App Inventor to play the app and remix the code. Choose Project > Import project (.aia) from my computer to open the source code of someone else’s app.