Everyone has pages that are useful to him and he has them at hand. Here is my list:
1. www.ppmm.pl
A lot of useful information, the site first helped me with my studies, and now I look at it at work.
2. Fanuc
3. Heidenhein
https://www.heidenhain.pl/pl_PL/dokumentacje/
https://www.heidenhain.pl/pl_PL/software/
https://www.klartext-portal.com/en/
4. Mitsubishi Electric
5. Siemens
https://www.biblioteka.siemens.academy/home
https://new.siemens.com/pl/pl/produkty/automatyka/systemy/cnc-sinumerik/sinutrain.html
https://new.siemens.com/global/en/markets/machinebuilding/machine-tools/cnc4you.html