Slavic languages are part of the Balto-Slavic family of Indo-European languages. They constitute three major linguistic groups: Western, Eastern, and Southern.
Western Slavic Languages
Eastern Slavic Languages
Southern Slavic Languages
As for the alphabet, the traditionally Catholic Slavic nations use the Latin alphabet (usually with diacritics because Slavic languages have more than 26 sounds), while the traditionally Orthodox nations use the Cyrillic alphabet developed by the students of Cyrill and Methodius as a simplification of the glagolitic alphabet created by St. Cyrill.
Notes:
The Serbian and Croatian are usually listed together as Serbo-Croatian because the differences are smaller than those between various dialects of the English language. The main distinction is that the Serbians are traditionally Orthodox and use the Cyrillic alphabet, while the Croatians are traditionally Catholic and use the Latin alphabet.
Moravian is not codified as other languages are. It is an interesting transition between Czech and Slovak, which changes gradually: In Western Moravia it is almost Czech, in Eastern Moravia it is almost (Western) Slovak.