One of the good points is promoting yourself.

People used to work with advertising company when they want to make commercials or promote something. But nowadays if you want to do that, then just go on social network sites. It means social networking can help us to show information. 

However, it has downsides too. The information on the social network can be used in a bad way like crimes. Because the photos or comments are important personal information, some scammers could approach the people as if they know the people.

After that, they may ask some money.

=> Corrected: The sentences are corrected grammatically.

-제가 쓴 글 좀 읽어봐 줄 수 있어요? Can you please read my essay? -> I was wondering if you would read my article for me.

-이 기계를 어떻게 작동 시켜야 하는지 알려주시면 감사하겠습니다.

It would be appreciated to let me know how to operate this machine.

->I'd appreciate it if you would teach me how to operate the machine.

-그래요, 간단한 일이에요

Yes, it's easy thing. ->Sure, it's a simple task.

=> Another way: Your sentences are okay and these are other ways of saying them.