Determine tensor of inertia of a rod

[Like Tony Stark]

Homework Statement

The pictures show two rods of homogeneous mass $m$ and length $l$. Determine their inertia tensors.

Relevant Equations

Matrix of inertia

I have to find the inertia tensor of these rods and I don't have the concept that clear...
I mean, I know the formulas like:
$I_{xx}=\int y^2 + z^2 dm$
$I_{xy}=\int xy dm$

But I don't know what $x, y, z, dm$ stand for. In other words, I don't know what I should replace in the formula with.

Can you do one example for me? Just one, like "in the first picture, if you want to calculate $I_x$, where you have $y$ you have to replace with b because that's..., and where you have $z$ you have to replace with 0 because..."

And what would it be the difference if these pictures didn't show rods but cylinders or another shape?

Thanks

 

[haruspex]

The general principle is that dm is a mass element at some (x,y,z), so if the density there is $\rho$ then $dm=\rho dxdydz$. Substituting that gives you a triple integral for each tensor component,
Given that this is just a rod, it will probably be more convenient to introduce ds as a length element and use a mass per unit length density. Expressing the coordinates as functions of s should give you single integrals.