Here is the complete content for the assignment:

```python
# This Python code will read from a text file, process its content, and write the output to another text file.

# Step 1: Reading from a source text file
input_file = 'input.txt'  # the name of the input file
output_file = 'output.txt'  # the name of the output file

try:
    # Step 2: Open the input file for reading
    with open(input_file, 'r') as file:
        # Read the content of the file
        data = file.readlines()

    # Step 3: Process the content of the file (for demo, we will just convert it to uppercase)
    processed_data = [line.upper() for line in data]

    # Step 4: Write the processed content to the output file
    with open(output_file, 'w') as file:
        file.writelines(processed_data)

    print(f"Processing complete. Check the '{output_file}' for the output.")

except FileNotFoundError:
    print(f"Error: The file '{input_file}' does not exist.")
except Exception as e:
    print(f"An error occurred: {e}")
```

### Explanation of the Code Line by Line:

1. We define the names for our input and output files.
   - `input_file`: the name of the file from which we will read data.
   - `output_file`: the name of the file to which we will write the processed data.

2. We use a `try` block to safely attempt to read from the file and handle potential errors.

3. We open the input file in read mode using a `with` statement, which ensures proper management of file resources.

4. We read all lines from the file into a list called `data`.

5. We process each line in `data` by converting it to uppercase and store the results in `processed_data`. This is done using a list comprehension.

6. We open the output file in write mode and write the processed data into it.

7. Finally, we print a success message to indicate that processing is complete.

8. In case of an error (like the file not found), we catch that with an exception and print an appropriate error message.

### Running the Code

To run the code, we would need an `input.txt` file with some text content in the same directory. When we execute the above script, it processes the data and creates an `output.txt` file with the text converted to uppercase. 

### Sample Input File (`input.txt`)

```
Hello World
This is a test file.
Python Coding is fun!
```

### Sample Output File (`output.txt`)

```
HELLO WORLD
THIS IS A TEST FILE.
PYTHON CODING IS FUN!
```

This is the complete content including the code and the expected output file's content.