How to represent a 2D Matrix using a Linked Nodes Data Structure

I want to know how to represent an upper Triangular Matrix using Linked Nodes data structure to store only the non zeros values with c++. The question tells me It uses “column nodes” to store matrix values, and “row nodes” to link the different rows together, and to access all “column nodes” of a particular row. It also says: Each row or column node contains an indicator to the corresponding row-index or column-index of the matrix.**
My Question is can anyone suggest me a starting point on how to represent the 2D Matrix using linked nodes. I really need a starting point to this question as I don’t know how to begin with it. thanks for the help.