Hi,

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

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

REST API

REST API is mainly used for  ease of integration and development. It supports smaller sets of data.

SOAP API

SOAP API cab be written in any language that supports Web services.
For example, you can use SOAP API to integrate Salesforce with your organization’s ERP and finance systems, deliver real-time sales and support information to company portals, and populate critical business systems with customer information.

Bulk API

Bulk API is based on REST principles and is optimized for loading or deleting large sets of data.
Bulk API is designed to process data from a few thousand to millions of records.
The easiest way to use Bulk API is to enable it for processing records in Data Loader using CSV files. This avoids the need to write your own client application.

Metadata API

Use Metadata API to retrieve, deploy, create, update, or delete customizations for your organization. The most common use is to migrate changes from a sandbox or testing organization to your production environment. Metadata API is intended for managing customizations and for building tools that can manage the metadata model, not the data itself.
The easiest way to access the functionality in Metadata API is to use the Force.com IDE or Force.com Migration Tool.


Thanks,
Allways Cool