Firstly, go onto any search engine, such as google, yahoo, msn, etc. and start searching for diamond stud earrings. You will find very many websites that sell diamond stud earrings. Write down which websites you liked so you remember to go back to them.
Step2
Once you have the websites that you liked you need to decide on your budget. When you decide what you want to spend start comparing prices from all these sites. Also, make sure to compare the qualities with the prices. You will need to weigh your options and decide if you want to spend rather on size or quality. Size -- Carat size- this will make a difference on how large the diamond studs will appear. Quality -- Clarity and Color. The better the clarity the more the diamond will sparkle. To learn more on quality visit www.DiamondStudSource.com They have an extensive section for diamond education.
Step3
Lastly, once you have compared the prices you need to make sure that the diamond are certified. The diamonds need to be certified so you can make sure that the information provided by the seller is accurate and true. The best labs in the US are GIA and EGL. Additional good labs are AGS, IGI, GIL, etc.
Tips & Warnings
Make sure that the diamonds from the earrings are not treated diamonds. Treated diamonds are stones that had some work done on them.
Make sure that when you receive the earrings that you receive the certificate too.
Novice 
