The standard way to add additional attributes to Shopify product data is to use Metafields.  Metafields are quite flexible with many supported data types.  You can also attach custom metafields to individual product variants.

However, to add metafields to your Shopify data, you'll need to do this either via the Shopify API or use another app as there's currently no option to add metafields in the Shopify Admin.

An alternative option for adding additional product attributes is to utilize the product "Tags" field (note that you can only add tags to products and not to individual variants).  If you just need to add a few additional attributes to each product, this is a simpler way to do this.

A common use case for adding additional product attributes is for generating product feeds for other platforms such as Google Shopping or Facebook.

For example, you might want to add a "Condition" and "Google Category" attributes to each product.  You can add a tag in this format to do this: Attribute Name: Attribute Value.

This way, you can easily identify which tag is which.  Here's what this would look like in the Shopify Admin:

Once you've added a new tag, this also becomes available in the auto-complete option so you can quickly add it to other products:

To export these tags in separate columns with EZ Exporter, you can then use a formula like this in the Calculated Fields:

search_list(to_list({{ tags }}), "Condition:", return_all_results=False).replace("Condition:", "").strip()

What this formula basically does is search the list of tags for the text "Condition:" (i.e. the attribute name) and then return just the value after that text.  You can then just copy/paste this formula and simply replace the attribute name to individually export the other attributes.

The output will then look something like this:

This blog post only covers the formula for EZ Exporter but you can probably use a similar formula in Excel or Google Sheets as well to parse the tags and pull out specific ones based on the attribute name assigned to them.