From Shaiya Wiki
A character's class is specific to their Race. Depending on which class is chosen, that character will only be able to use certain Equipment and Skills.
List of Classes
Classes are considered to either be strong in a Party or played Solo. For example, a Defender/Guardian has very high defence, but a low attack and a Pagan/Mage has a low defence but a high attack. If the two classes party, they can use their strengths to have both the high defence and the high attack to defeat their opponents. Solo classes generally have a more balaced defence and attack and do not depend so much on being in a party. This does not mean they cannot or should not party, only that they would not significantly benefit either way.
The play style of each class may also be effected by the build a player chooses. Using skills and spending Stat Points differently may change their ability to solo or not.