This August, I've got to go from Rome to Calabria Calabro (Stazione),
and I'd like to know which form of transportation would be easiest.
And, where is the main Train & Bus stations located in Rome?
By train, and even then it will take about 8 hours. You can do a timetable search for yourself for the date (or at least day of the week) you want to travel, e.g. on the trenitalia website (or any other, e.g. http://bahn.hafas.de/bin/query.exe/en), but one possibility involving only one change is dep. Roma Tiburtina 14:20 arr. Paola 19:58, dep. 20:25 arr. Corigliano Calabro 22:23; or with very similar timing (last train is the same one from Paola arr. CC 22.23), you can leave from Roma Termini at 14.45, with an additional change at Napoli Centrale.
You can see Rome stations on this map - Termini is at the intersection of the blue and orange lines and Tiburtina a few stops up on the blue one: http://www.romebuddy.com/givesadvice/subwayroutes.html
Contrada Thurio, Corigliano Calabro
Loc. Fabrizio Piccolo, Corigliano Calabro
Via dei Clementini, Lido Sciavonea, Corigliano Calabro
Via Armando Diaz, Corigliano Calabro