How to create Custom setting and retrieve the records from Custom setting object and its feilds.

Step 1: Create New Object in Custom setting.
Step 2: create new custom Fields what you require.
Step 3: Create records in Custom setting object in "Manage"

use the following code in the apex classes to get values

  list<(custom object api)> trtd = (custom object api).getall().values();

for Example:

list<US_Holidays__c> trtd = US_Holidays__c.getall().values();