How to create a Sandbox org for existing developer org.here is the link https://help.salesforce.com/apex/HTViewHelpDoc?id=data_sandbox_create.htm&language=en_US but i dont find any sandboxes link in Setup section.Please guideline how to create a sandbox for developer org.is there any difference between test org and sandbox.
You cannot create a sandbox from existing developer org. But you can create a sandbox from an existing production org. Also, you can create a developer sandbox box from the production org. By default you can create a developer sandbox which is free one. The other sandboxes which are developer pro involves a cost.
Usually developer org used to create managed and unmanaged packages separately. whereas Sandboxes used to create enhancements like trigger, vf pages, components, crm modules in sandboxes and push the changes to production.