In Milan, there are 5 metro lines and many underground and surface lines that can take you anywhere in the city. I highly recommend using the Moovit app, which will advise you on the public transportation to use to reach your chosen destinations more easily.

You can also use the web version:

https://moovitapp.com/index/it/mezzi_pubblici-Milano_e_Lombardia-223

If you need to take a taxi, always choose regular white taxis, so you won't have any surprises.