Change sprite images on button click

This is my first time making anything in Unity and I've been trying for days to figure this out and I just can't. What I want to be done is super simple and yet nothing is working.

Basically, I placed buttons on my 2D landscape, with the intention of the player clicking on these buttons and having a sequence of images/sprites appear in order with every click (there are 5 images/sprites to appear total)

The other basic action I need to have is clicking on an image/sprite that will make another image/sprite appear on the screen.

I'd say that to put a reference on how this game is played, think of a super simple dress up game where clicks make the item appear on the character being changed

It all sounds so basic and it's frustrating me that I haven't been able to get the code right. If anyone can help that would be great