I think that Added Effect Materia is for status magic, say for instance you have Added Effect equiped to your armor with say silence it might make you resistant to silence and I know what Elemental Materia does: if you have Fire linked with Elemental in your sword then your attacks would do fire damage and if you have it in your armor then your armor would be fire resistant the higher level the elemental the higher the restence 1* halfs damage 2 for Nul damage and 3 for absorb (I think)