Warcraft Gold is necessary for us to play in the game, and we will value it.
Here you can see your creature stats and also spend runes of magic gold in order to level up creature skills. It is recommended to level up Exp and JP Acquisition Rate Increase skills whenever you can. To use active skills that only the creatures can use, drag the skills from the creature skill window onto the creature quick-slot bar placed right above your character quick-slot bar, and use it from there like you would with your character.
Of course, you can buy rom gold to create skills even more quickly, and than you will have long time to play. The list of all the skills of specific creatures can be found on this site. When your creature reaches a certain level, you can evolve the creature to strengthen it even further.
When you evolve a creature, it will change its name and appearance, and will be reset to level 1, but keep all the skills it has earned previously. It is similar to how characters change the job class.
The first evolution can take place at level 40, and the second at level 50, however you can over breed them by leveling them further before you evolve them in order to pick up more skills and make them stronger.
It takes very long to over breed the creatures, so do it only if you have all the time in the world and have much patience. To evolve your creature, talk to the Tamer NPC and choose creature evolutes.