First, open your Google Sheet and navigate to the "File" menu. Select "Download" and then choose "Comma Separated Values (.csv, current sheet)" to export your data as a CSV file. This format is easy to work with and can be directly read by many programming languages.

Ensure you have MongoDB installed and running on your local machine or server. If not, download and install it from the [MongoDB official website](https://www.mongodb.com/try/download/community). Start the MongoDB server by running the `mongod` command in your terminal or command prompt.

If you plan to use Python for this task, ensure that you have Python installed on your system. You will need the `pandas` library to read the CSV file, and `pymongo` to interact with MongoDB. Install these libraries using pip:
```bash
pip install pandas pymongo
```

Use the Pandas library to read the CSV file you exported in Step 1. This can be done by executing the following Python code:
```python
import pandas as pd

data = pd.read_csv('path_to_your_file.csv')
```

MongoDB stores data in a BSON format, which is very similar to JSON. Convert the DataFrame you created in Step 4 to a list of dictionaries (JSON format):
```python
data_json = data.to_dict(orient='records')
```

Use the `pymongo` library to connect to your MongoDB instance and insert the data. Here's how you can do it:
```python
from pymongo import MongoClient

client = MongoClient('mongodb://localhost:27017/')
db = client['your_database_name']
collection = db['your_collection_name']

# Insert data into MongoDB
collection.insert_many(data_json)
```

After inserting the data, it's a good practice to verify that the data has been correctly stored. You can do this by querying the MongoDB database using the MongoDB shell or by writing a small Python script:
```python
for document in collection.find():
print(document)
```

By following these steps, you can successfully move data from Google Sheets to MongoDB without relying on third-party connectors or integrations. Make sure to adjust file paths, database names, and collection names as needed for your specific situation.