Synthetic aperture radar is basically building a bitmap of radar reflectivity. So what you get looks a lot like a photo. You can end up with very non-photo artifacts though - blown out pixels caused by corner reflectors, bright things can result in ghost copies in multiple places and if there’s other radar operating in the same frequency bands it can end up on the picture.

The core idea is that you send out pulses as you pass over the ground and then record the echoes. You can create an image by - for each pixel in the image - working out the response you would expect to receive back and correlating that with the actual responses you saw. That gives you a reflectivity value. You can do it in multiple polarisation to better distinguish things.

What you can get in a single image are 5.5cm wavelength microwave backscatter - this means surface materials can be differentiated by looking at texture differences at that scale. So - tarmac vs a ploughed field, for example. There's 2 polarizations as well, so you can identify e.g. vegetated areas also, which scatter the signal in a different way.

A single image from Sentinel-1 won't give a height map directly, but a pair can using interferometry (InSAR), as the phase of the backscattered signal is also measured. With that you can derive something about the terrain. It's not super accurate though for absolute height maps.

And yes the signals pass through cloud and it works at night.