The Netherlands has a very efficient system of public transportation. In Rotterdam, you will find national trains, light-rail, a metro system and various bus routes. The national rail service is called NS and you can plan your journey via their website. They also have a mobile app. The light-rail, metro and bus services are all operated by private companies. You can plan your journey on their websites as well or use the more popular 9292 site. This site combines all forms of public transport in the Netherlands.
To travel on NS, you must have pre-purchased a valid ticket/OV Chipcard before your journey and conductors may check your tickets. It is still possible on some bus and rail lines to purchase tickets on the spot, however it is much more common to use an OV chipkaart. These cards are accepted on all forms of public transportation. You must have a minimum balance on your card to use it. Cards can be linked to your bank accountant for automatic recharging. They can also be used to rent bikes at the NS stations, known as OV fiets. There are various discount and subscription opportunities with NS as well as other public transportation providers.