Product specifications are extremely useful in describing a product's attributes. There are only limited # of fields such as Title, Description, SKU, or GTIN to describe a product. An infinite number of specifications allows us to attribute or define a product in many ways; similar to custom fields. 

For example, let's say you sell T-Shirts online and every shirt requires at least a color, size, material, country of origin, and whether it's machine wash safe. Simply create a specification for each attribute and the product page with list all specifications. Product comparison would make it easy for customers to compare shirts of different material and country of origin. Product filtering using Refine By Widget would allow customers to only view red shirts, that are available in Large size, and are safe to machine wash. 

Let's say we want to add a color specification to our T-Shirt Product.

To add a product specification: 

1. Create new product or Edit an existing one
2. Click New Specification from Specifications section
3. Select a Specification. For this example, let's select Color. Create new specification if you don't see it in the list. 
4. Select Catalog Option from Options. 
5. Select the option from Catalog Option. For this example, let's select Red. Update a specification if you don't see the option in the list. 
6. Click Yes for Allow Filtering if you want customers to filter on this specification in Refine By Widget. Click Add
7. Repeat step 2 to 6 to add additional specifications. Click Update

Use Custom Text  
When you don't want to create a new option in Catalog > Specifications. For example, let's say this particular shirt has a custom "Electric Green" color which would not be used in any other product. In such case, you don't have to Update a specification and add a new option; instead, you can change Options to Custom Text and type "Electric Green" 

Use Custom HTML Text 
Similar in use as Custom Text option but allows you to include HTML. Change Options to HTML Text and use the HTML Editor.

Use Link
You may have specifications that link to another resource. For example, you may be selling a product that has a manufacturer datasheet. In that case, change Options to Link and paste the link to the datasheet.