Attributes are mostly used as advanced user fields for webshop/API. They can be also used to add value to product for example: kitchen_item and bar_item. Attributes can be imported with whole products import or separately

Create Excel table with attributes and their values. Mandatory fields in table are product code and attribute.
Format all cells to text and save as .xlsx file

Navigate to PIM -> Product Importer. Add the file and configureit. 
More specific information can be found in our Product Importer guide. 

Under Mappings, choose the right attribute. In this example it is Int attribute. Import file.

Check your attributes in PIM