Centralstation
Centralstation (take a wild guess at an English translation!), is at Olof Palmes Plats.
I would've said that Olof Palmes Plats and the Busstation are on Kungsgatan, but actually, they're on Stadshusgatan, a rather insignificant road running through Järnvägsparken, a narrow green in front of the train station.
There is branch of Pressbyrån inside the station building where you can buy a Busskort.
There quite are a number of of red internet terminals inside in corrals on the southeast side of the main concourse (to the right if you enter via the main entrance).
Directions
From Stora Torget, walk 3 blocks (~200m) southeast down Kungsängsgatan, the pedestrianised street with Åhléns on the corner. Turn left up Bangårdsgatan, the first street you come to with vehicular traffic on it, and walk 2 blocks (~175m) northeast. You will see the train station on Olof Palmes Plats a short distance in front of you. Total distance: ~400m.
