Metafields + is an amazing app to attach custom fields, apart from what Shopify allows you to.
You can add custom meta-fields to:
Type of Metafields you can attach:
Edit meta-fields directly from products, variants, collections and customers admin page by clicking on "More Actions" > "Edit via Metafields +"
Bulk Import/Export Meta-fields via CSV
Examples of custom meta-fields:
Attach Self-Assembly instruction files for your products/variants
Attach Size Charts
Link internal production files
Your imagination is the only limitation to what purpose you use these custom meta-fields, over your Shopify Store.
Simply follow instructions from app on how to show custom meta-fields on your store front.
No advance Shopify Liquid knowledge required.