Nested document

Elastic Stack Elasticsearch
1

Hi,

I try to create 'test' document as follows

{
"test": {
"properties": {
"nested_docs": {
"properties": {
"user_id": { "type": "string", "index":
"not_analyzed" },
"user_name" :{................}
"created_time": { "type": "date" }
}
}
} } }

I have a field 'nested_docs' [multi-valued] which has two fields
[user_id, created_time].

Will this document mapping automatically be nested type, or do I have
to specify "type": "nested" ?

Also i would like to know about the advantage of using nested
documents.