Making a starry landscape photograph has 5 main steps:
Find a time and place with an interesting foreground beneath a star-filled sky.
Capture a set of images of the scene. The camera must be in a fixed position on a tripod and all of the exposures must be identical. At least 10, probably not more than 40 images should be captured.
(Optional) Convert the images from RAW to TIFF.
Align and stack the images with Starry Landscape 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.