Everybody knows, now chatter widget is available to collaborate with the peoples or a group of people in your company. To enable the chatter widget to the users you should have "Customize Application" permission, if you have this permission follow the below steps.
Your Name-->Setup-->Customize-->Chatter-->Chat Setting
Now you are on the page to enable the chatter widget.You can see there is a two option
1. Chat Setting.
2. Visualforce Setting.
Click edit and check true in 'Enable Chat' under chat setting, then users in your company can chat with each other by using chat widget,This actually enables chat widget.To verify whether its enabled or not click on the home tab in that bottom right corner you can see like below image
if you click on this image you can see the list of people whom you follow and your favorites list.
The second one is 'Visualforce Setting' if you enable this then chatter widget will display on the Visualforce page also if you didn't then you can't able to see the chatter widget on Visualforce page.
To display the on visualforce page then in the page also you need to add one more attribute "Showheader=ture".
But if you don't header but not chatter widget the you need to use two attribute on the apex:page tag
Now it will work fine,I think it will useful for you.