To start using api, you need to do 4 simple steps:
Go to the access keys page and add private apps. Details about access keys.
Go to the api keys page and create a new key. Details about api keys.
Go to the cache page and wait for the primary caching process to complete. Details about cache.
Go to the documentation page and see the list of available methods. Details about documentation.
After these steps api is completely ready to work with your store.