Here is a example of a Group/Rank with GroupManager

groups:                               <--- Heading of groups file
 default:                             <--- Name of group
  default: true                       <--- When someone joins do they get this rank of not
  permissions:                        <--- What can they do
  - essentials.ban                    <--- Permissions from a plugin (Essentials)
  - essentials.op                     <--- Permissions from a plugin (Essentials)
  inheritance:                        <--- Will they have the same commands as another group
  info:                               <--- this is were you put there stuff
   prefix: '&a[&eDefault&a]&e'        <--- What will they have infront of there name
   build: false                       <--- can they build
   suffix: ''                         <--- What comes after there name

And once you make it make sure it works copy and paste it in this sight and see if you get any errors http://yaml-online-parser.appspot.com/