All About Custom MetaData Types | The Salesforce Developer Guide

Custom metadata is packageable, adjustable, upgradeable, and deployable application metadata. To start with, you make a custom metadata type, which characterizes the type of application metadata.

Points of interest of Custom metadata: 

• Page configuration can be used in Custom metadata types. 
• Endorsement Rules can be used in the Custom meta-type. 
• We can make Lookup associations with other custom metaData types like custom things. 
• We can make adequately picklist fields in custom metaData types. 
• There is no Governor limit in the SOQL question. 
• Datastore in-store memory which expands the presentation of the association. 
• Custom metadata types are recognizable in test class without the "SeeAllData" comment. 
• Custom metadata are intelligible for all profiles, remembering the visitor client for a public case. 
• 50,000 records are returned for each exchange through Custom metadata.
• There is no restriction for SQL inquiry per exchange. 
• 100 records or fields for each custom metaData.

The distinction between Custom Metadata and Custom Setting

Custom Metadata: 

The size of Custom metadata records can't be 10MB.

100 records or fields for every custom metaData. 

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Custom Setting:

No inquiry needed in custom Settings. 

Custom setting is anything but difficult to get to. 

Custom setting permits distinctive information for an alternate arrangement of a client by various leveled custom setting.

Only 300 fields allowed in a custom setting.

Tab cannot be created in custom settings.

How to add custom metadata in your org:

1. Go to set up in your org and search for custom metadata.

2. When you reached the screen, click on new.

3. Enter the fields according to your naming convention. 

4. Save.

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Now, after saving it you can add the fields and validations rules if need to require. Enter the custom fields values, and add details.

Like this, you can add the custom fields. It comes in handy when you have multiple values of the fields and required to use them in the code.