This tutorial to create virtual environments suggests, that I should add these commands to my .bashrc file:
eval "$(pyenv init -)"
eval "$(pyenv virtualenv-init -)"
On the home directory of my macOS, when I check for ls -a, I do not see a .bashrc file. I do see however a .zshrc file. Is this an alternative? Can I put the commands here or should I create a new .bashrcfile in my home directory using nano or similar?
You should run echo $0 to check which shell you're using, but I would be fairly certain no .bashrc means no bash shell in use. If you're using a later version of macOS then zsh will be in use already as the default shell (but bash is in use on older versions pre-Catalina by default).
If echo $0 does output bash or /bin/bash rather than zsh or /bin/zsh then you should create a .bashrc file and put the commands in it - but if your output contains zsh, then you should put the commands in the .zshrc file already in existence.
Yes, this is the file you want to edit if you're on a mac. .bashrc is a configuration file for the bash shell (an extremely common shell, often assumed to be the ubiquitous shell). This file is sourced every time you start a new shell (running all the commands within). On mac however, the default is zsh, which uses .zshrc as its configuration file.