Begin by exporting the data from your "cart" system. This could be in a format such as CSV, JSON, or Parquet, depending on what the system supports. Ensure that you have the correct permissions to export data and that you understand the format and structure of the exported file.

If you haven't already, install DuckDB on your local machine. You can download the appropriate version for your operating system from the DuckDB official website. Follow the installation instructions for your system (e.g., using a package manager like Homebrew for macOS or an installer for Windows).

Once you have the data exported from the cart system, check the file for any necessary pre-processing. Ensure data consistency, correct formatting, and that there are no missing values that could lead to errors during import. Make adjustments as needed.

Launch DuckDB and create a new database where you will store the imported data. You can do this by running the following command in your DuckDB shell or script:
```sql
CREATE DATABASE 'your_database_name.db';
```
Replace `'your_database_name.db'` with your desired database name.

Define the schema of the table in DuckDB to match the structure of your data file. Use the `CREATE TABLE` statement to create a table that mirrors the columns and data types of your export file. For example:
```sql
CREATE TABLE your_table_name (
column1_name column1_type,
column2_name column2_type,
...
);
```

Use the `COPY` command in DuckDB to load data from your file into the newly created table. For a CSV file, the command might look like this:
```sql
COPY your_table_name FROM 'path_to_your_file.csv' (FORMAT CSV, DELIMITER ',', HEADER);
```
Adjust the parameters based on your file's format and delimiter. Ensure the path is correctly specified.

Execute a simple `SELECT` query to ensure the data has been imported correctly:
```sql
SELECT * FROM your_table_name LIMIT 10;
```
Check that the data appears as expected. If there are any discrepancies, revisit the previous steps to adjust the file or import settings.

By following these steps, you can successfully move data from your cart system into DuckDB without relying on third-party connectors or integrations.