Most of the website owners have a desire to know about the visitors to their sites. There are some ways to find this information such as:

Server Log Analysis
Mostly all web servers maintain a record of the files that they send along with the requests received. These requests are sent by the user's browser. It includes his IP address, name of the browser among others. The IP address is the most important of all this. 

The IP address is helpful in the identification of the ISP and the location of the user. It also helps in identification of a number of unique visitors as compared to the number of pages that were loaded overall. This helps to know the number of times a visitor re-visits your site.

There are some softwares that can extract the information from the servers logs and transform them into graphs and tables. Most web hosts have these softwares.

Cookies
IP address of a single ISP looks as if all visitors are the same. To find unique visitors, it is required to leave a cookie with a random ID number on the visitor's computer. This helps you to find whether that user has been to your site before or not.

By a count of the number of unique visitors, you can know the number of visitors who have visited your site. However, many users have cookies turned off on their systems. So this is not a completely reliable method.

Registration
To get detailed information about your visitors, you can make them to register and log on to your website. This helps you to collect their emails, location and anything else that you want.

But everyone is not willing to give your their phone numbers and address so easily. If you ask for registration too early, then it would drive your visitors away.

Surveys
Survey is an alternate for registration. It is used by most companies by means of pop-up ads followed by a series of survey questions.

Its advantage is that since there are no personal details required for surveys, the visitors are more willing to answer personal questions that they would otherwise be unwilling to reply to.