You can simply copy the CosmeticsMod.jar into the .minecraft/LabyMod/addons-1.8 folder. To find the .minecraft folder, press the Windows key + R and enter %appdata%.
No, all Cosmetics that you adjust via CosmeticsMod are only visible to you! Online Cosmetics can only be purchased in the LabyMod Shop: labymod.net/shop
Unlock the Cosmetic GIFCAPE, click the gear icon and then Open Folder. Here you can insert .GIF files and press Reload Textures ingame. Now all you have to do it enter the file name into the text box and the animated Cape should be visible!