Is there a rest api to get parties(Organizations)

Summary

REST api to get organizations, its accounts and sites

Content

Setup and Maintenance -> manage customers -> Search with Organization Name.

I have followed the above navigation. After searching an organization, I get respective accounts and sites for the particular organization.

Can you please let me know how to achieve the same via REST api?

1.REST API to get Organizations loaded into my instance

2.REST API to get accounts of organization

3.REST API to get sites of organization

Note : I am trying to create a Salesorder via REST API. To do so, I need bill-to,shipt-to details for which I need the organizations via REST