Java APIs

Hello,
I' m doing an application using java but I needed to connect to a remote machine. I have access to that machine. I use a socket to make the connection with this machine. But since it's not working I'm trying to understand why its not working. I read that someone in this site says that "... sockets can not be opened from outside " if this is really how sockets work I understand why I' m not have any sucess.

But I really wanted to know if this is true, and if there's a way that a socket could be used to make a remote connection. Or if you could tell me what is the method used for doing this because I found so many topics about remote connection but I don't know what method I should use.

I'm using Linux.

Thank you in advance,