Pytest Installed, but VS Code Won’t Access Pytest

[snippsat]

What command should I use to download pytest to a particular folder that contains python?

You shall not download at all,this is all done bye pip.
Open cmd and test python and pip command.

C:\Users>cd ..

C:\>python -V
Python 3.11.3

C:\>pip -V
pip 23.1.2 from C:\python311\Lib\site-packages\pip (python 3.11)

C:\>

So it most work like this,if not you most fix you environment variables path.
Then will pip install pytest --upgrade download and install automatic to this Python 3.11.
When this work on command line as posted before in VS Code down in right corner Python interpreter(choose same version).

e.g. if the test file were calculation.py, when I type import calculation, it comes up with the same error, namely that import "calculation" could not be resolved

That's different when use own modules file most be in Python sys.path or run from same folder as code.