OP took 3600 pictures of 1 second exposure each ( the sensor capture light particles for 1sec for each picture )

Then OP takes all 3600 pictures to a stacking software ( we don't know which one OP chose, but there are many like SiriL, DSS, etc )

The software will align all the pictures using the stars. Then it'll average out every single pixel ( ie. pixel in the same location in the sky, hence why it needs to align the pictures )

The stacking process will reduce the noise created by the camera sensor ( and there is a looooot of it ), and keep what we call signal ( so the actual light from stars and galaxies and stuff ) at roughtly the same level.

When seeing a 1sec exposure, you will think there is litterally no light from the galaxy that reached your camera, but it did ! It's so low that it's almost black ! Keyword here being ALMOST black, so it's there !

Once the noise has been removed by stacking, you take your stacked image ( only 1 file usually in .tif/.fit format ) and process it in a software like Photoshop, gimp and so on.

Now you just need to carefully use "level adjustments" and "curve adjustments" ( not sure about my grammar of adjustments ) to bring all the data in the near-black to the grey/dark-grey zone, and you're basically done !

Hope it helped ! I didn't go too much into the explanation because I tried to keep it as simple as possible ! Astrophotography is a really nice ( but becomes expensive ) hobby, I suggest you to take a quick look into it !