Are there any really basic tutorials for getting started on creating your own shaders? Like, very basic, from the top sort of stuff? The unity documentation isn’t really a tutorial.
Really basic tutorials for Cg vertex and fragment shaders:
http://en.wikibooks.org/wiki/Cg_Programming
I didn’t adapt the tutorials to Surface Shaders yet. And I’m not sure I will because it is more complicated to explain stuff with Surface Shaders as a lot of functionality is implicit that has to be explicitly coded when you write Cg vertex and fragment shaders; thus, for teaching it is easier to work with the explicit Cg code. Once you understand Cg vertex and fragment shaders, Unity’s documentation about Surface Shaders is OK.
And, yes, it’s also OK if you disagree. 
Thankyou, reading now
Also, this is probably a very basic question, but how do I open shaders in Unity? If I go Right click > Create > Shader, and then double click it, it doesn’t open. Help? Is this just me, or am I not doing something correctly?
It should open in MonoDevelop by default, but really any text editor will do fine.
As farfarer said, it should open. However, opening MonoDevelop often takes a lot of time.
Jessy “Tutorial Shader” on Youtube. : http://www.youtube.com/user/JessyUV 
Good point; I usually forget that “shaders” in Unity include configurations of the fixed function pipeline.
I’ve found these videos to be invaluable http://www.youtube.com/user/animate4evr