Does anyone want to help me out on Substance Designer?

@Slaytexify Can you post a link to your graph and I can take a look at it

Dave

Most likely you don't have any outputs defined or they are not named in a way that can auto map.

Easiest way to just check everything is working and get going is open empty graph, hovering over the graph hit space bar and search for base material add that to the graph.

right click and hold down right click and drag, you should see a little texture square under your cursor.  drag and drop that on to the 3d model, that will automatically map all the outputs and apply the base material.

play with the sliders in the base material get a feel for what they do.

then to get a feel for what a fairly standard prb set of output look like right click on that base material and select create output nodes, don't create all the hidden ones, if you right click hold and drag one of those over the model it will ask you what channel to apply it to and you can experiment with that.

finally to start with I would enable some basic inputs on the base material and use those to start experimenting and plugging stuff in this will make your model go black because it override the default sliders in the base material and you haven't plugged anything in there yet.  for convenience you can just do the right click drag on the base material even with the nodes coming off it.  Over time you will create your own node groups to be more exact for what you want.

Unless it's an "atomic" node which just means it's compiled with no node tree, one of the best ways to learn is look at how the nodes are constructed.  If you take the base material node for example, if you right click on it and open the reference you can see how that node is created, 

for this example you can even ctrl a and copy the displayed node tree and paste into your graph and edit it / play around etc.

to clear the materials to start again I just do it from the viewer , if you have multiple graphs open it can be a bit confusing what material is applied as it will swap depends on what graph has focus.