When you are doing something you want to know if it working or not. The same thing with website or some application you want to know how many people using it. Fortunately there are some tools to provide that data in some reasonable statistics view. I’m mostly using Google Analytics tool.
Its popular and well documented tool which is built and ready for almost all cases you can imagine within measuring user activity on your website. Can provide really nice overview on all devices or deliver statistics on regular basis
Example of user sessions in Google Analytics