What is Yammer?
Yammer is as easy to use as great consumer software like Facebook and Twitter, but is designed for company collaboration, file sharing, knowledge exchange and team efficiency.
How to switch from SharePoint Online Newsfeed to Yammer?
By default, the SharePoint Newsfeed is your Internal Social Network.
Now this can be changed to Yammer and here is how:
First Sign in to Office365 portal using a global admin account and navigate to SharePoint.
From SharePoint Admin center click on Settings and change the Enterprise Social Collaboration from default to Use Yammer.com service.
Once the change is saved you should be able to see that the SharePoint Newsfeed link is replaced with a link to Yammer.
This update could take up to half an hour in my case it took about 6 minutes.
How do users sign in to Yammer?
Yammer.com is a separate service from Office 365 and requires separate account credentials. Microsoft is working on single sign-on authentication, but it’s not ready yet, so how do users sign in?
If your users already have Yammer.com account they can sign in with their Yammer accounts and if not, they can sign up for free (if you’re a Microsoft Enterprise Agreement customer).
What happens to the Newsfeed?
When your organization switches to Yammer, SharePoint Newsfeed functionality doesn't go away. People can still access Newsfeed from their Sites page, and they can continue to follow SharePoint sites, documents and tags there. However, they no longer have the option to send a message to everyone.