In default, Shopify not allow you add new custom field for product. So with Elessi we will help you understand how to bring custom field to your store.
Example: you can have different short descriptions, different size chart... for each product.
Go to Dashboard Settings > Custom Data > Select type of Metafield > Add definition button to start configuring Metafield. Kindly follow my video below:
1. Countdown
Namespace and key: meta.countdown
Select Content Type: Date and time > One value

Go to Products > Metafields > enter a value for metafield option:

Go to Theme customize > add 'Countdown timer' on product page and see the result:

2. Short description
Namespace and key: meta.description_excerpt
Select Content Type: Single line text or Multi line text

Go to Products > Metafields > enter a value for metafield option:

Go to Theme customize > choose 'Short description' on product page and see the result:

3. Size chart
Namespace and key: meta.image_size_chart
Select Content Type: Single line text
Go to Products > Metafields > enter a value for metafield option:
Go to Theme customize > choose 'Short description' on product page and see the result:
4. External/Affiliate
Namespace and key: external.Buynow (Buynow text will be shown on the button)
Select Content Type: Single line text

Go to Products > Metafields > enter a value for metafield option:

The result: