Well, what do you know then?
Do you know how to create a window?
Do you know how to use an event loop?
Do you know how to deal with the sf::Event::MouseButtonPressed?
Do you know how to increment a variable?
The tutorial covers each of these things (except the incrementation, but this is more than the basics of programming
) and this is all you need.
What don't you understand, and what do you already have? If you haven't even tried before asking for help, then you're using the internet wrong.