Here are some articles about creating this Service Application. Both with UI and PowerShell.  I like the first one.

http://www.lamber.info/post/2010/12/05/How-do-I-create-a-new-managed-metadata-service-application.aspx

I faced a small issue during setting up the MMS.

My Setup consists of

1 Front End Servers

1 Application Servers,

1 SQL Server 2012

1 Workflow Server

1 WAC Server

1 AD Server

All the setup has been done in least permissions with different service account.  I started the MMS Web service from Manage Service on Server Page.  Then went on to create MMS Service Application with least permission.  On Visiting the MMS Service Application page I saw the error. 

Message “The Managed Metadata Service ‘Managed Metadata Service Application’ is inaccessible.”

Event ID: 8080

Task Category Taxonomy

Another error in log was

 

Event ID: 8077

Message “There are no instances of Managed Web Service is started on any server in the farm. Ensure that at least one instance is started on an application server in the farm using the Services on Server Page in Central Administration.”

Solution:

Your SharePoint Admin Account or System Account that you are using to browse the Central Administration does not has access to service Application so

Go to Manage Service Applications Page

Select Managed Metadata Service Application Row

From Ribbon Click Permissions

Now Add your Admin account contoso\SP_Admin in my case.  Click Add and give him all 3 permissions and click OK.

Better to do an IISRESET

Now try to access it again.

It took me some time to get it back. 

Here are some guys talking about the same issue.

http://sharepointknowledgebase.blogspot.com/2012/09/the-managed-metadata-service-or.html