What was the nature and extent of the Umayyad Empire?
You could start out with where and how large this empire was.
How did the Abbasid Empire differ from the Umayyad Empire?
Make two lists -- one including the features of the Abbasid Empire and one including the features of the Umayyad Empire. Once you do that, you should be able to clearly see how they were similar and how they were different. Write about the differences.
What were the achievements of the Arab phase of Islamic development ending in 750?
1. Go to http://www.google.com
2. Type in achievements of arab phase of islamic development to 750 AD (or whatever search terms you need). Press Enter.
3. Read different search results until you find what you need.
4. Re-search with different search terms if you don't find all you need.