When I was university student = When I was still a univesity student, I went to USA 11 years ago. It was my first long and oversea trip = It was my first long and overseas trip ; Note: the sentence is correct but take not of your spelling "overseas" not "oversea" (highlighted word). So I prepared 3 month for this trip. = So I had prepared for 3 months for this trip. (You have to use had + verb  because it is a past event or it happened a long time ago)
I was interesting because all ones were fresh. Food, Foreigner, and the other things are fresh to me. = It was interesting, because everything was new to me, the food, foreigners and others. / It was interesting, because everything was new to me. (Note: Instead of using fresh, it is better to use new; fresh can be used to describe food or flowers and replace all to everything, because it fits the thought of your sentence)
I had Uno Pizza which is famous pizza in Chicago. = I had Uno Pizza, a famous pizza parlor in Chicago.  Especially, I drunk kocktail and saw night view in skylounge of John hankok tower. = During my visit in the U.S., I also drank a cocktail, and had seen the night view at skylounge of John Hankok Tower.
I can not forgot the night view when I look on the skylounge. = The night view at skylounge was very memorable to me, because...(You can also supply or explain why it becomes memorable; this will make your sentence more detailed.)
And I went to Saint Louis and illinois university by rental car. = ...Illinois University by a car rental (Don't forget that Illinois is a proper name of a place so the first letter should be capitalized)  It was my first driving in USA. = It was my first driving experience in USA. I felt little bit sared but threr was no accident. = I felt a little bit scared but I haven't met any accident. Anyway I had good experience and trip. So, I think this trip is my most favorite trip. = I had a good experience in the U.S.  That's why it is my favorite trip. (Avoid using the word "trip" from one sentence to another, because it makes the thought repetitive. You have to think of another word that is synonymous or similar to trip, example: travel, adventure, etc.) 

Corrections Guide:

blue wrong sentences = red the corrected sentences

Remarks:

Please take note of the corrections made.  I'm glad that you did your homework. I appreciate your effort in writing and expressing your thoughts in your most memorable trip.  Way to go Jay!  Keep it up! :)