Depending which terminal you start from it’s about 10 minutes by train to either the Keisei Narita Station or the JR Narita Station.
Both Narita stations are close to each other. The Keisei Narita line tends to have more frequent and slightly faster connections.
Cost each way is around 250 to 270 JPY.

If you plug your date and departure or arrival time into https://www.hyperdia.com along with “Narita” and whichever of the Narita Airport options corresponds to your terminal you can find the times you needs. Just take note of whether it is the Keisei or JR station for each option.

Keep a note also of the times and options for when you expect to arrive and head down to the corresponding platforms at the airport. They are well sign posted and you will see different entrances for the different rail companies. If it isn’t clear to you, Keisei is probably the more convenient choice.