I strongly advice against the use of code from Coding Made Easy, especially regarding networking. The creator has very limited knowledge in C++, even less in SFML and near zero in networking.
If you want to learn how networking is done right, you should go read the official SFML tutorial, look at the example that ships with SFML, go read all the topics in the official FAQ and once you did all this and still have open questions, you should go and search for binary1248 forum post here in the Network section.
Networking is not an easy topic and it's important to learn things right and not just write something without even having the slightest idea what it does and pray that it won't crash.
Also make sure to follow the
general rules for posting, which includes for instance "Give details" or "Identify the problem (a.k.a "complete and minimal code")".