opening price is not same as the previous close because after trading hours there is news or data related to company which affects the market price of the share on the next day opening price. opening price might be higher or lower it depend upon the news.
It depends on many, these factors are very important especially if you handle forex or some currency exchange, it is very important to learn them so that one has the necessary knowledge to know how to act you can find more information by the link and above all that it will be very helpful learn all this.
I think that for this you do not need to have a higher economic education. I recommend that you just gain experience and read more information on the Internet. Maybe video reviews on YouTube will help you. I also advise you to read https://marketbusinessnews.com/factors-steer-global-economy/260849/. So you can get to know the economy better.