A) Import:

1. Click on the Import button, it will show the Open-As window.
2. Select the OBJ file that you want to import. 
3. A new document will be opened automatically and OBJ file data will be imported into that document.  

B) About: 

    It displays information about the product and the facility to activate your product license at any time.

The installer that ran when you downloaded this app/plug-in from the Autodesk App Store will start installing the app/plug-in. OR, simply double-click the downloaded installer to install the app/plugin. You may need to restart the Autodesk product to activate the app/plug-in. To uninstall this plug-in, exit the Autodesk product if you are currently running it, simply rerun the installer, and select the "Uninstall" button. OR, click Control Panel > Programs > Programs and Features (Windows 7/8.1/10/11) and uninstall as you would any other application from your system.

1. Limitation in size of the OBJ model to be imported (not consistent). Large models are not imported in Revit
2. Mesh import may not work for all the meshes in OBJ files. Sometimes meshes are not imported correctly
3. There are no different faces. The whole model is one surface.