Usually, global attributes are created and managed via the "Classes & Attributes" section (Catalog -> Classes & Attributes) of the store Admin area.
To view the list of global attributes configured in the store, open the "Classes & Attributes" section and click on the link "Edit attributes (N)" opposite the "Global attributes" line (where N stands for the number of global attributes configured in the store).
The global attributes listing page allows adding new and managing existing global attributes and grouping global attributes if required.
To add a new global attribute:
In your store’s Admin area, go to the "Classes & Attributes" section (Catalog > Classes & attributes).
Click on the "Edit attributes (N)" link opposite the "Global attributes" title.
A page where you will be able to manage global attributes opens.
On this page, click "New attribute:"
A popup titled "New attribute" appears:
Use the fields of the "New attribute" popup to provide information about the new attribute. Specify the following information:
Attribute: Attribute name.
Attribute group: Select a group name from the drop-down if this is applicable. Use the Attribute Groups guide to learn how to join attributes into groups.
Type: Attribute value type (Plain field, Textarea, Yes/No, Hidden field).To choose a proper attribute value type for your attribute, refer to the guides from Attribute Value Field Types.
Display as: Select the display mode from the drop-down.
Click "Next." The popup expands to edit attribute options:
Configure the attribute options depending on the chosen attribute value field type. Then, add as many attribute values as you need.
If you want any of the option(s) to assign automatically to all NEW products in your store's catalog, click the check-mark icon opposite the names of the related attribute options (the check-mark icons should turn green):
Enabling a check-mark for a hidden attribute option will not affect the existing products by far. All existing products will preserve their current global attributes' configuration.
When complete, save the changes using the "Save changes" button.
All global attributes are assigned automatically to all existing products in the store. However, to be appropriately displayed in the storefront, a store admin must configure global attribute options for existing products.