MongoDB is not like a typical relational database management system (RDBMS). Instead of adding columns, you can add fields or entire documents to a collection in MongoDB.
However, if you want to insert a new field (think of it as a kind of adding a column) to every document in a MongoDB collection, you can use the update() method with the $set operator.
Here is an example:
```
db.collection_name.update_many({}, {$set : {“new_field”: field_value}})
```
In this example, `collection_name` is the name of your collection and `new_field` is the name of the field you want to add, `field_value` is the value you want to set for this field. This will add this field to every single existing document in the collection.
If you want to add a field to a specific document, you just replace the `{}` (which selects all documents) with a query that matches your desired document(s), for example by `_id`.
Remember, MongoDB has a flexible schema so each document in a collection can have a different set of fields. This operation will not prevent you from adding or removing additional fields (columns) from individual documents.
Please note, MongoDB shell uses JavaScript as a scripting language so the tasks are performed using JavaScript functions. If you are using Python, PHP, or any other language as a language driver, you will have to use the respective language syntax to achieve the tasks.
