I'm not a Lightroom user, but from what I can see in images of the HSL module, it gives you sliders to adjust hue, saturation, and lightness independently for different "bands" of the color spectrum. The color zones module in darktable provides a similar functionality, but the interface presents an adjustable curve rather than sliders.

An important thing to know from the start is that you can vary the "width" of the adjustment by scrolling the mousewheel over the circle showing the adjustment point. The color zones module also has the additional feature of allowing you to move the adjustment points along the spectrum (by dragging the triangles). This can give more precise control in the areas where you want it, but since there are only 7 points vs. 8 sliders, you may have to move them from their default positions to get them to correspond to the particular sliders in Lightroom that you want to emulate.

Essentially, the darktable color zones module has the same relationship to the Lightroom HSL module that a parametric equalizer has to a graphic equalizer.