How do I start buying diamonds?

I'm interested in purchasing diamonds but I'm not sure where to begin. Could you please explain the process of how one goes about starting to buy diamonds? What steps should I take to ensure I make an informed decision and get the best value for my money? Are there any specific factors I should consider when choosing a diamond, such as its cut, clarity, color, and carat weight? Additionally, how can I be sure I'm buying from a reputable and trustworthy source?