@User i recommend going here for the open_pdks installation and follow the Download and Install sections. You may watch this , For ngspice clone the sources using git:

git clone <https://git.code.sf.net/p/ngspice/ngspice>

, then follow the instructions in README and INSTALL. I have also video explaining how to install xschem and ngspice, however to NOT follow this video for the skywater-pdk part since this is covered in the newer open_pdks video posted above.