# How to interpret band structures

I'm currently taking a Solid State Physics class, and is currently reading about the quantum mechanical description of solids.

I then came across the following figure:

It's supposed to be the band structure for aluminium. My question is basically: How do I interpret these band structures ? I can't even see why they cut of the region from $X$ to $\Gamma$ at the dotted line in the first figure, and not in the second :/ Why is the last bit of $X$ to $\Gamma$ that you see in figure 2, not important in figure 1 ?

I understand that, the $X$, $\Gamma$, $K$, $L$ and $W$ are points of symmetry on the brillioun zone. But what does it mean for the electron(s) ? Only that they have higher energies at some points ?

I'm just having some trouble understanding what this band structure tells me, and what I'm able to see/do with it ?

So can anyone maybe explain it, maybe even easily, what I actually have to understand when I see this ?

As you have already stated, the polyeder in the upper part of the figure is plotted in 3D k-space and visualizes the first Brillouin zone. The dotted line nicely visualizes a closed (one-dimensional) path in k-space that -- by convention -- runs through the special points you already mentioned. Now, this closed path is precisely the horizontal axis in the lower part of the figure (this is why it starts and ends with $\Gamma$) and what is plotted in this figure is the energy dispersion $E(\vec{k})$.