To launch an activity in android using the adb shell, you can use the following:
adb shell am start -n com.example.package/com.example.package.ActivityClass
To avoid having to write the main package, you can do this
adb shell am start -n com.example.package/.ActivityClass
If you are already within an adb shell session, you can just do
am start -n com.example.package/com.example.package.ActivityClass
# or
am start -n com.example.package/.ActivityClass