Both tools remap tonal values in the image, but Curves gives you more control.

Levels is the simpler adjustment: it works like a straight-line remapping from black to white. You mainly set the black point, white point, and midtone brightness, which changes the overall slope of that tonal mapping.

Curves does the same basic job, but it is more flexible. Instead of being limited to a simple straight-line adjustment, you can place points and shape the curve to affect specific tonal ranges independently. That means you can brighten midtones, deepen shadows, or protect highlights with much finer control.

So, Levels is essentially a simpler subset of what Curves can do. If you want a quick global tonal correction, Levels is often enough. If you need precise control over contrast and luminance in different parts of the tonal range, use Curves.