you better look for a basic Material tutorial. Nodes in Materials don’t have the same functionality like in Blueprints and sadly they often have very different names displaying than they have in the search bar. Also you’ll get the very same Material function multiple times in one search result, because it’s registered in multiple categories (I guess nobody came around to fix that?).
For your random in range problem:
There is no simple function for that in the material editor (unless you use instances or particles) Usually I use the noise node wich outs out a single value based on a Position (Vector3)… better look for another tutorial there 
To get the oragne box:
- the searchterm is “Constant3Vector”
- either double click the black square in the node to set another color or set it to the right in the details panel (as you have selected that node)
the color you see there is a preview of what the node will put out. You can minize the node by clicking the small white triangle in the top left corner of the node.