What is the use of Metadata API in Salesforce?

Hello saloni,

Use Metadata API to retrieve, deploy, create, update or delete customization information, such as custom object definitions and page layouts, for your organization. This API is intended for managing customizations and for building tools that can manage the metadata model, not the data itself. To create, retrieve, update or delete records, such as accounts or leads, use data SOAP API or REST API.

you should refer to this Link :

https://developer.salesforce.com/docs/atlas.en-us.api_meta.meta/api_meta/meta_intro.htm

Hi,

Use Metadata API to retrieve, deploy, create, update or delete customization information, such as custom object definitions and page layouts, for your organization. This API is intended for managing customizations and for building tools that can manage the metadata model, not the data itself. To create, retrieve, update or delete records, such as accounts or leads, use data SOAP API or REST API.

The easiest way to access the functionality in Metadata API is to use the Force.com IDE or Ant Migration Tool. Both tools are built on top of Metadata API and use the standard Eclipse and Ant tools, respectively, to simplify working with Metadata API.Force.com IDE is built on the Eclipse platform, for programmers familiar with integrated development environments. Code, compile, test, and deploy from within the IDE.
The Ant Migration Tool is ideal if you use a script or the command line for moving metadata between a local directory and a Salesforce org.
For more information about the Force.com IDE or Ant Migration Tool, see developer.salesforce.com.

The underlying calls of Metadata API have been exposed for you to use directly, if you prefer to build your own client applications. This guide gives you more information about working directly with Metadata API.

You can use the Metadata API to manage setup and customization information (metadata) for your organizations. For example:

Export the customizations in your organization as XML metadata files. See Working with the Zip File and retrieve().
Migrate configuration changes between organizations. See deploy() and retrieve().
Modify existing customizations in your organization using XML metadata files. See deploy() and retrieve().
Manage customizations in your organization programmatically. See CRUD-Based Metadata Development.
You can modify metadata in test organizations on Developer Edition or sandbox, and then deploy tested changes to production organizations on Enterprise, Unlimited, or Performance Editions. You can also create scripts to populate a new organization with your custom objects, custom fields, and other components.
Thanks