I have downloaded Esri web appbuilder now I want run it but I'm stuck here in the URL.
You must have either a named user account that belongs to an Organization, or a Developer account to connect Web AppBuilder too. See this help link: https://developers.arcgis.com/web-appbuilder/guide/getstarted.htm specifically this section:
Specify your portal URL
Note, if you do not have an account, you can sign up for a free trial or setup a developer account:
If you don't have an ArcGIS account, sign up for an ArcGIS free trial or the ArcGIS Developer Program.
To get an AppID for Web Appbuilder review the next section of the help link above which is titled
Provide an app ID for Web AppBuilder.