[2021] help please

Here's the Store page:
https://store.steampowered.com/app/1531470/Cities_Skylines__Content_Creator_Pack_Train_Stations/

If you mean ingame, then you are looking for the CCP tab, which is highlighted here:
https://i.imgur.com/jcDIMj9.jpg

For the Train Stations pack it's at the end of the public transport menu.