To begin, you need to access Trello's API. First, log into your Trello account and navigate to the Trello API documentation. Create an API key and token by following the instructions provided. Ensure you store these credentials securely, as you will use them to authenticate your API requests.

Use the Trello API to fetch data from your Trello boards. You can do this by sending a GET request to the Trello API endpoint for boards, lists, or cards, depending on the data you need. Use tools like `curl`, `Postman`, or write a simple script in Python or any language that supports HTTP requests. For example, in Python, you can use the `requests` library to make a GET request using your API key and token.

Once you receive the data from Trello, it will typically be in JSON format. Parse this JSON data to extract the specific fields you want to move to MongoDB. You may want to clean and structure the data at this stage, ensuring it's organized in a way that aligns with your MongoDB schema.

Ensure you have a MongoDB database set up where you can insert your Trello data. You can set this up locally or use a cloud-based MongoDB service like MongoDB Atlas. Create a new database and define collections that will store the Trello data, ensuring they have the appropriate structure to accommodate the parsed data from Trello.

Write a script to establish a connection to your MongoDB database. If you're using Python, you can use the `pymongo` library. Install this library using `pip install pymongo` if you haven't already. Use the connection string provided by your MongoDB instance, and authenticate if necessary, to establish a successful connection.

Use the parsed JSON data from Trello to insert documents into the MongoDB collections. Map each field from the Trello data to the appropriate field in your MongoDB collection. Use the MongoDB driver from your language of choice to perform the insertion. For Python and `pymongo`, you can use methods like `insert_one()` or `insert_many()` depending on the volume of data.

After the data insertion process is complete, verify that the data in your MongoDB collections accurately reflects the data from Trello. This can be done by querying the MongoDB database and comparing a sample of the data to ensure consistency. Also, check for any errors or discrepancies that may have occurred during the data transfer process.

By following these steps, you can manually move data from Trello to MongoDB without relying on third-party connectors or integrations, providing you with full control over the data transfer process.