Ensure you have access to the Teradata environment with the necessary permissions to read the data. Install the Teradata CLI or any client tool that allows you to execute SQL queries and export data from Teradata.

Use the Teradata BTEQ tool or SQL Assistant to export the required data into a CSV or JSON file. Execute a query to select the data you need and redirect the output to a file. For example:
```sql
.EXPORT FILE=/data.csv;
SELECT * FROM your_table;
.EXPORT RESET;
```

If you exported the data to a CSV file, you may need to convert it to JSON format, which is more compatible with MongoDB. Use a script in Python, Perl, or any language of your choice to read the CSV and output JSON. For example, a simple Python script using `pandas` might look like:
```python
import pandas as pd
df = pd.read_csv('data.csv')
df.to_json('data.json', orient='records', lines=True)
```

Ensure MongoDB is installed and running on your local machine or server. You need access to the MongoDB server with permission to insert data into the desired database and collection.

Use the `mongoimport` utility to load the JSON data into MongoDB. Run the following command in your terminal:
```sh
mongoimport --uri="mongodb://localhost:27017" --db your_database --collection your_collection --file data.json --jsonArray
```
Ensure that the database and collection names are correctly specified and that the file path to `data.json` is correct.

Access the MongoDB shell or use a client like MongoDB Compass to verify that the data has been imported correctly. You can execute a simple query in the MongoDB shell:
```js
use your_database;
db.your_collection.find().limit(5).pretty();
```
This command checks the first few documents in your collection to ensure the data looks correct.

If this data transfer is a recurring task, consider writing a script that automates the export, conversion, and import processes. You can use a combination of shell scripting and cron jobs (on Unix-based systems) or Task Scheduler (on Windows) to schedule regular data transfers.

By following these steps, you can successfully move data from Teradata to MongoDB without relying on third-party connectors or integrations.