Salesforce Communities are available only when Salesforce1 interface is opened in a mobile browser. As of now, Communities cannot be accessed in the "app" itself, and this is still on the roadmap for Salesforce1 app for a future release.
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In your org, under Setup | Mobile Administration | Salesforce1 | settings, check "Enable the Salesforce1 mobile browser app" and click Save. Now try opening in a mobile browser through login.salesforce.com. If you still cannot see the Salesforce1 interface in the mobile browser, try opening with login.salesforce.com/one/one.app
Salesforce Communities are available only when Salesforce1 interface is opened in a mobile browser. As of now, Communities cannot be accessed in the "app" itself, and this is still on the roadmap for Salesforce1 app for a future release.
If this answers your question, please mark this as the Best Answer for this post, so that others can benefit from this post.
Thanks,
Shashank
could you please explain how to open interface for salesforce 1 in a mobile browser.
Regards,
GM