Sept 1 , purchase a camera--- Step 2 , take photos--- Step 3 , develop the negatives------------ Step 4 , ________
The specific steps would typically require addtional hardware such as a scanner.
There are flat bed scanners that are capable of scanning from photo-negatives, and the scanner usualyy comes with software for inverting the colors- thus converting the scanned image into a positive one.
I offer the following link to a video of one technique in which someone converts a negative image into a positive.
If they are old slide and/or phot-negatives, I can see purchasing a scanner to get the job done. But what perplexes me is the reasoning for the first 3 steps you mention, when a digital camera would eliminate the need.
Yet at the same time I realize the question as a valid one - if nothing more than the curiosity of how it would/could be done. If the video does not give you insight into the steps and the equipment required, I would be more than willing to attempt to help answer the question in more detail - just let me know.