from list of entries, select and add to scene beneath previous

I'm new to scripting and such, i've been scouring google and I can't seem to find an answer or road to the answer that I understand. What it seems like I want to use is a list of pre-defined gameObjects, and have it displayed onto the canvas somehow.

Example of what I want to do:

• Press 'add member button'

• overlay with list of selectable characters displays

• find in that list desired character, select it.

• overlay goes away and the entry is now displayed on the left of scene in panel using predefined size

• repeat previous steps, and have 2nd and subsequent characters be placed beneath the previous.

Examples of what I mean in shotty paint mock-up: