Cape For My Guild !

I have a cape for my guild, however I cant use because it says I need a emblium. How do I do this and where ?

At the guild emblemer, once you leave presearing ascalon (if that's where your character is) or arrive at any of the major cities, Lions Arch, Kamadan, etc, there is an NPC that will let you select an emblem for your cape. The cost is 2 plat each time you change it (though the interface will let you try all sorts of combos before you actually save one and pay the 2 plat)