How to store a list of three numbers in a list

Im trying to create a function where I can store three elements in a list. Im using these three elements to create a horizontal line wherever i want. First, it stores the first element which is the starting x, named a for now. then the second element which is the length of the line, named b for now. This makes the domain a < x < a + b. and finally c represents the height.

Not sure your need for the list (and this really is a question), but here’s a few ways to make a dynamic line.