Elasticsearch murmur3 template

Question

How to use murmur3 hash? Can you please give a sample with comments of each fields.

I have read the documentation on https://www.elastic.co/guide/en/elasticsearch/plugins/current/mapper-murmur3-usage.html and they gave a sample like these:

PUT my_index
{
     "mappings": { --> what is these?
    "my_type": { --> what is these?
      "properties": { --> what is these?
        "my_field": { --> what is these?
          "type": "keyword", --> what is these?
          "fields": { --> what is these?
            "hash": {
              "type": "murmur3"
            }
          }
        }
      }
    }
  }
}

Please also include on how to use it on GET.