IV.New activity_main.xml file is opened the go to projectname->src->package_name->MainActivity.java
V.This is an helloworld activity it will create automatically every time you will open an new project.
VI.To run this you need to create an emulator from the icons you have AVD manager.
VII.Open that and new give name of the emulator and give the resolution and click save snapshot if u want it stores installed apk you open the emulator next time. give create avd.
VIII.Then click on your avd and give start.emulator open.wait until it will finish the process.
IX.Then Right click on project->Run as->Run Configurations->select project->apply ->run.