NS:
NS is the train transport used in the Netherlands. By train you can easily and quickly get to Amsterdam, but also to other cities!

Tickets:
The easiest way is to buy tickets via the NS.nl app, which also saves you €1 because you do not have to print the tickets.
You can buy day tickets, single and return tickets on the app.
This can also be done via the site: https://www.ns.nl/
You can also plan your journey on this site, so you can see exactly where you need to go and what time the trains leave.

GVB:
GVB is the organization that regulates trams, buses and metros in Amsterdam.

Tickets:
The easiest way is to buy tickets via the GVB app or website. On the app you can buy day tickets, single and return tickets. This can also be done via http://the site: https://reisproducten.gvb.nl/en/travel-products/hour-and-day-tickets/gvb-day-ticket

On this site ->http://https://www.gvb.nl/en/travel-information/journey-planner you can also plan your journey, so you can see exactly where you need to go and at what time which transportation option departs.