How I can create user defined roles

I have a database in mongoDB 2.6.4 in which I want to restrict the users as per their level. I want to give read privileges to some users and insert/update privileges to some other users on a particular database. Please let me know how I can create user defined roles and assign them to the users. I tried the below but it is not working; the users still have full privileges:

db.runCommand({createRole: "read",

   privileges: [

         { resource: { db: "sample", collection: "" }, 
                     actions: [ "find" ] 
           }],
   roles: [],

   writeConcern: { w: "majority" , wtimeout: 5000 }

             })

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db.addUser( { user : "read",
              pwd  : "read",
              roles:["read"]
        } )