I have globally installed modules in my pc, but when i create a virtualenv some of the modules are already preinstalled in it, but when i execute 'pip freeze' in my virtualenv there are no installed modules. commands like django-admin , cookiecutter already work in my virtualenv though i have never installed them in it. But other commands like numpy or pandas do not work , though i have installed them in my machine globally like django or cookiecutter. How do i fix this? I am using python version 3.9.6.
TL;DR: The django-admin and cookiecutter commands are accessible from your virtual environment because they are on PATH. This isn't related to the Python virtual environment, but rather due to your whole system. If you want to make global packages accessible in your virtual environment, see this answer.
django-admin and cookiecutter are executables. They're located in some folder on your system (most likely the Scripts folder of your Python installation), and that folder is in PATH. Therefore, the shell can access them, no matter if you are in a virtual environment.
To contrast with that, numpy and pandas are only libraries. Therefore, when you try to import them in your code which is run in the virtual environment, they cannot be accessed. This can be changed by either installing them in the virtual environment, or including system site packages, which you can see how to do in this answer.
If you tried to import django or cookiecutter, that wouldn't work either (in your virtual environment), just like numpy or pandas. There's no way to "fix this", because it isn't broken. I wouldn't suggest removing Scripts from PATH, because that would mean those commands would never be accessible.