Before exporting data, ensure that you have the necessary access permissions to the Teradata database and tables. Verify that you have access to the Teradata SQL Assistant or any command line interface like BTEQ (Basic Teradata Query) for executing SQL queries.

Use the Teradata SQL Assistant or BTEQ to export the required data from Teradata. You can execute a SQL query to extract the data you need. Save the output as a CSV file or another text-based format that MongoDB can easily read. For instance, you can use:
```sql
.EXPORT FILE=
SELECT * FROM your_table;
.EXPORT RESET
```
Ensure the data is well-formatted and clean for subsequent import into MongoDB.

Once you have the data in a CSV file, examine its structure to ensure it aligns with MongoDB's document model. Make any necessary adjustments to the CSV file, such as renaming columns to match MongoDB's field names or formatting data types appropriately.

Ensure that you have MongoDB installed on your machine. Additionally, install MongoDB tools such as `mongoimport`, which is a command-line tool used to import content from a CSV file into a MongoDB collection. You can download these tools from the MongoDB website if they are not already installed.

Before importing data, create a new database and collection in MongoDB to hold the data. You can do this through the MongoDB shell or using a GUI like MongoDB Compass. For example:
```shell
use myDatabase
db.createCollection("myCollection")
```

Utilize the `mongoimport` tool to import the CSV file into the MongoDB collection. Specify the database, collection, and type of file being imported. Here is a sample command:
```shell
mongoimport --db myDatabase --collection myCollection --type csv --file --headerline
```
The `--headerline` option tells `mongoimport` to use the first line of the CSV file as field names.

After the import process, confirm that the data has been imported correctly by querying the MongoDB collection. You can use the MongoDB shell or a GUI to run a simple query and review the data:
```shell
db.myCollection.find().limit(5)
```
Check for data integrity and ensure that all fields are correctly populated.

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