How to get the skill ID?

[ywwow]

I am a junior on mod writing.I noticed that there were item id and skill id.Now many mods can show item id,and we can use it in macros and so on. But how about the skill id?I know it can be found at some wow database websites,but how do they get this information?And is there other way to find a skill's id?

I hope my poor English have stated my meaning clearly.Eagerly waiting for your help!