Hello Amir,
Seems like you did not compile the plugin .dll, or the plugin is not enabled.
Follow the instruction on the link below to compile the plugin:
http://www.unreal4ar.com/getting-started-full-version/
a. Windows
- Install Visual Studio 2015 – community editions are also working
- unreal engine editor
- Create a new C++ code project without starter content
- Copy all files from SampleProject directory to your new project directory
- In UE4 editor File -> Refresh visual studio project (optional)
- Exit from unreal engine editor
- your new project from epic launcher
- Click on rebuild missing DLLs when prompted