Salesforce has powerful CRM features. In order to extend this features, we go for Web Service API.

Steps to define API in Salesforce:

1. Go to Setup menu.
2. Develop –> API

Bulk API:
Used to create, retrieve, delete and update large amount of records.

REST API:
Mainly used for integration. It also maintains passwords.

Metadata API:
Mainly used for migration from sandbox to production.

SOAP API:
Used to create, retrieve, delete and update records.