Hi Anu! This is what I thought:
"I want to learn to speak English very well. My first and most serious reason is to understand all foreign countries people in the world.
My second reason is for cultural awareness, and that I want to travel all over the world.
My third reason is that I would like to live in USA where there are many people from other different cultures"
However, if I were you , this is what I would say:
"I want to learn to speak English well for 3 reasons. First and foremost, to understand all foreigners in the world as English is one of the most widely-used languages. Secondly, I wang to travel all over the world. My third reason is that it would be great to live in USA where there are many people from different cultural background."
Overall, good job! Cheers!