All buses, city buses as well as remote buses, leave from the Central Station. In the Central Station you also find Kalmar Resecentrum, with information about timetables and prices, and here you can also buy tickets for the bus traffic.
Kalmar länstrafik is the bus company that operate within Kalmar city, but also throughout the county, from Västervik in the north to Berkvara in the south, with Oland in between. Good to know is, that you can only buy a ticket on the bus with a debit card, alternatively bus pass. It is not possible to pay cash on the bus.
If you want to travel outside Kalmar there are several options with the remote buses. Silverlinjen has a direct bus between Oland-Kalmar-Stockholm with daily departures. During the summer there are three daily journeys in each direction.
Flixbus has an extensive route network in Sweden and abroad, and Kalmar has several daily trips from Stockholm.