If you want to add a long description to a product in the product module, open the product and click on the pencil in the top right hand side next to description.

In the next screen you'll also see a slider allowing you to add the long description to quotations. If you choose "Yes", the long description will be used whenever you add this product to a new quotation. 

Remarks:

• To edit the description when creating your quotation, simply click the symbol with four horizontal lines next to the product line:

• Make sure you've added the shortcode $LONG_DESCRIPTION$ to your quotation template to show the description on your quotations. 
• If you want to add the long description of a product automatically to your invoice or order, you need to activate this in your Settings:
  • Go to Settings > Products > Preferences 
  • To add the long description to your invoices, enable 'When adding a product to an invoice, include the product description'
  • To add the long description to your orders, enable 'When adding a product to an order, include the product description'