Convert Lead to deal and pull through product

Convert Lead to deal and pull through product

Good day, 

When i create a lead there is a custom field where I indicate which product they are intersted in. When I convert a lead into a deal I would like it to indicate/link the product to the deal in the "product" section of the deal. 

I tried it with mapping but no luck. Appreciate any help. 

The step after thatwould be to have the deal amount automatically calculated based on the products. But that is step two. 

Kind regards, 

Bryce