There are daily buses to Kalambaka from Athens and Thessaloniki via Trikala. The bus from Trikala also connects Kalambaka with other villages in the region. From Kalambaka, there are buses and taxis up to the Monasteries of Meteora. Once you have reached one monastery, you can walk to the other as they are a relatively close one to the other.
Many visitors also go to Meteora by tour from Athens and Thessaloniki or by private means. There are no car rentals in Kalambaka, so if you want to drive there, you will have to do it with a rental car from another town.