When you choose to create propositions you will come to the image below.
You can choose to add products from the following alternatives: Products, Old orders, Based on a campaign or Existing propositions. 

You can also choose to insert an empty row if you want to categorize your products in the proposal.

To delete or insert a blank row afterwards, select that row and swipe left.

Select on the line of the product if you want eg. change the quantity.

If you want the proposition to apply to the entire chain, check "Chain"
If it only applies to the customer, you leave it unchecked.