Making a starry sky photograph has 5 main steps:
Find a place with clear dark skies and chose a part of the sky to photograph.
Capture a set of images of the sky. The camera must be on an equatorial mount and all of the exposures identical. I recommend at least 50 images, but capturing several hundred is reasonable.
(Optional) Convert the images from RAW to TIFF.
Align and stack the images with Starry Sky Stacker.
Finish the image with your favorite image processing tool such as Photoshop or Affinity Photo.
Steps 2 through 4 are discussed in detail below. You can find many tutorials, both free and paid, on the web that will help with both step 1 and step 5.
Shooting for Starry Sky Stacker