Some basic reasons of rejection of the articles are :-
1. The article quality is not good. There are lot of grammar or English or spelling mistakes in the article
2. There is copy content in the article
3. The article summary is not good
4. The description of the article is not so good.
Read article guidelines before submitting the article
Since you are a new member, I suggest you to read and understand the Posting Guidelines with respect to different sections in ISC and also all the Help Topics before beginning to submit contents here. It goes without saying that one should get acquainted with the requirements of the site before becoming active so that the rules and policies are adhered to. Please go through a few of the earlier posts in different sections to get an idea as to how you should go about while posting contents here. It is not very difficult.
ISC is a very friendly site and you can look up to senior members and editors for guidance at any point of time by just posting a thread in the forum in case you face any problems even after reading the guidelines and help topics.
As for articles, this articles on Good Article Writing Tips will surely help you to understand the rules and also will help you to write better.
I suggest that it would be better if you concentrate on the forum for the time being and start by responding to new threads on topics that might be of interest to you. You can move on to other sections once you become familiar with the site.
Just spare a few minutes to know the site and start contributing by following the guidelines. All the best!
'Real knowledge is to know the extent of one's ignorance'- Confucius