|Plenty of ways, how depends on how and where your web site is hosted.|
If the site is hosted by a web hosting company then most of them provide facilities to log visitors.
If you host the web site yourself then Apache and IIS provide visitor logging. I imagine so do other web server software.
There is also remote logging avaliable where you insert a piece of code into you web site the automaticaly logs every vistor to a remote logging server. These usually cost money.
There is other software available that will analyse the web logs and give you a break down of of where, when, what and how. A search of Google will give you many options.