The unreal engine youtube channel has some good beginning tutorials (and some more advanced ones as well). Also check out the documentation which has a reference for nearly everything in the engine, including explanations for many of the material nodes. Also for materials, many UDK/UE3 material tutorials will still work in…
It will come with experience. Often times you'll watch a tutorial about a completely unrelated material to the one you want but you'll still learn something which can be transferred to something you want to do. Often times for a simple prop, all that's required is just the texture and there's no need for fancy shader…