Hi there. Anything that appears to be a weapon or armor piece in the Eververse Store is actually an Ornament—essentially a skin for an actual item. Universal Ornaments such as the Omega Mechanos set can be equipped by inspecting a piece of legendary (purple quality) armor that has an elemental affinity (specific element that corresponds to the types of mods you can use on that item), tabbing down to the Appearance menu, and selecting the Ornament from the customization slot. Other Ornaments such as those for weapons or exotics (yellow quality gear) can only be applied to their respective item.