Doubly Linked List Helper Functions

Apologies if this question may sound too trivial. I am trying to implement a simple DLL and would want to understand helper functions(such as insert,add elements,replace etc). Please let me know how I should go about this. If there is any weblink/slide material,it would be very helpful.

My ultimate aim is to represent univariate polynomials(yes it is an assignment) and would like to get started.