In the online application there is a special item in the menu, where you can add your Fulbright references. Three letters of recommendation are required. Even though it seems that this is the part of your application you can influence the least, I ensure you, it’s not! It is not only who you ask to be your recommender, but also how you approach and what you ask them to do, that counts.
I found a document Applying to Ph.D. Programs in Computer Science, written by Mor Harchol-Balter from CMU, where a section “Recommendations” gives very good advice on how to ace your recommendation letters.
How to Choose a Recommender?
I would advise you not to choose recommenders only because they are “famous” in their field of work. Unless your recommender is famous internationally among wide audiences there is little chance the reviewer will have ever heard about him. Choose people from your professional and academic life that know you not only through your grades but have an experience on what it is like to work with you. It is obvious that they should also be fluent in English.
As you most probably already know, people (especially the busy ones) are not very keen on writing recommendation letters. Sometimes they will ask you to write one yourself (for them to sign) or at least to prepare some points they should focus on. In this case, you should look at your application, project proposal, personal statement, and think of ways the recommendation letters could enhance the way you want to present yourself.
Once you add your recommenders to the online application, they will receive an email with explanation on how to upload their recommendation letters. They will also have to answer a few questions about your qualities (an online form), but there is not really a lot you can help them with there. If you chose appropriate recommenders and prepared them well, they should be able to do the rest!