public class UpdateContactPageLayout {
    // Add custom field to page layout
    
    public Metadata.Layout addLayoutItem () {
        
        // Retrieve Contact layout and section 
        List<Metadata.Metadata> layoutsList = 
            Metadata.Operations.retrieve(Metadata.MetadataType.Layout, 
            new List<String> {'Contact-Contact Layout'});
        Metadata.Layout layoutMetadata = (Metadata.Layout) layoutsList.get(0);
        Metadata.LayoutSection contactLayoutSection = null;
        List<Metadata.LayoutSection> layoutSections = layoutMetadata.layoutSections;
        for (Metadata.LayoutSection section : layoutSections) {
            
            if (System.equals(section.label, 'Additional Information')) {
                contactLayoutSection = section;
                break;
            }
        }
        
        // Add the field under Contact info section in the left column
        List<Metadata.LayoutColumn> contactColumns = contactLayoutSection.layoutColumns;     
        List<Metadata.LayoutItem> contactLayoutItems = contactColumns.get(0).layoutItems;
        
        // Create a new layout item for the custom field
        Metadata.LayoutItem newField = new Metadata.LayoutItem();
        newField.behavior = Metadata.UiBehavior.Edit;
        newField.field = 'AMAPI__Apex_MD_API_Twitter_name__c';
        contactLayoutItems.add(newField);
        
        return layoutMetadata;
    }
}

public class MetadataExample {
      
    public void updateMetadata () {
        Metadata.CustomMetadata customMetadata = new Metadata.CustomMetadata();
        customMetadata.fullName = 'MyNamespace__MyMetadataTypeName.MyMetadataRecordName';
        
        Metadata.CustomMetadataValue customField = new Metadata.CustomMetadataValue();
        customField.field = 'customField__c';
        customField.value = 'New value';
 		
		customMetadata.values.add(customField);
		
        // Create metadata container         
        Metadata.DeployContainer deployContainer = new Metadata.DeployContainer();
        
        deployContainer.addMetadata(customMetadata);

        Id asyncResultId = Metadata.Operations.enqueueDeployment(deployContainer, null);
        
	}
}