using CRM Visual Ribbon Editor - Edit the Ribbon add button to ribbon

You can add bottom with functionality to any entity in MS CRM.

1.) Before adding button to ribbon , Create a java script web resource and add a simple function

web resource name: new_getCustomerDetails

function getDetails(){

alert("here you go");

}

2.) Have a any button Image of 16x16 size and 32x32 size ready
button name: new_btnDetails - Upload as Image web resource.

3.) Now ready to add button to ribbon
Open ribbon editor by clicking VisualRibbonEditor.exe

And connect to CRM by passing credentials and URL

Once you successfully logged in to tool select entity to add the button.
it will load he corresponding entities ribbon on tool.

Once ribbon loaded Please select the group where you need to add the button.

Details Tab: click new button.and give name and label, Select the 16x16 and 32x32 image of button.

Action Tab: Select the the previously defined web resource: new_getCustomerDetails and give function name as  getDetails .

now save and export the solution.
and refresh the entity. you will see the new button.