Gems are socketed into your gear to give you boosted stats. They can be combined to create stronger gems. They are well worth buying as they can be reused again and again. If you cant buy them, then an HP one in each gear is a good strategy.
HP gem - Raises your hit points, this is good for any class and you should aim to have a high level one in each of your gears
MATK - Magic attack gem, use ONLY for mages. This little beauty means your mage packs an even bigger punch. A mage should have one of these on each gear.
PATK - Physical attack gem, good for archers and knights. A good amount of these is nice but exactly how many is dependant on what build you go for.
MDEF - Magic defense gem, ok for any class but mages probably wont need to use them and knights and archers can get away with just one or two if any.
PDEF - Physical defense gem, good for all classes. A few are always good. Mages will want to have a good number of these.
Crit Gem - Raises the critical chance. Archers love these but they are good for all classes. Knights and mages might want a couple of these socketed depending on build.
Block gem - Raises the amount of damage you can block. These may look like a good thing but it is better to invest in the above kinds of gems rather than these.
Charisma gem - Raises the troop count to make your troops tougher. You probably won't want these as the troop count can be raised other ways.
HP gem - Raises your hit points, this is good for any class and you should aim to have a high level one in each of your gears
MATK - Magic attack gem, use ONLY for mages. This little beauty means your mage packs an even bigger punch. A mage should have one of these on each gear.
PATK - Physical attack gem, good for archers and knights. A good amount of these is nice but exactly how many is dependant on what build you go for.
MDEF - Magic defense gem, ok for any class but mages probably wont need to use them and knights and archers can get away with just one or two if any.
PDEF - Physical defense gem, good for all classes. A few are always good. Mages will want to have a good number of these.
Crit Gem - Raises the critical chance. Archers love these but they are good for all classes. Knights and mages might want a couple of these socketed depending on build.
Block gem - Raises the amount of damage you can block. These may look like a good thing but it is better to invest in the above kinds of gems rather than these.
Charisma gem - Raises the troop count to make your troops tougher. You probably won't want these as the troop count can be raised other ways.