How to make an android app connect to server to give and receive information in real time

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http://stackoverflow.com – OK, so I am new to Android developing and to server connections as well and I would like to know if there is a simple and easy way that can allow an app to connect to a server of my choice and then be able to send and receive information from said server in real time. I also would like to know if making the server and app send and receive data from each other make the performance really slow or not. Thank you so much for all your help! (HowTos)