You find out how much traffic your site has by examining site logs which are kept by the Web server. Increasing traffic (obtaining more visitors to your site), however, is not as simple.
Web servers keep logs which list every single HTTP request that anybody made to your site. Using this information, you can estimate some useful statistics about the usage of your site.
If you wish to get more visitors to your web site, one thing you can do is ensure that your site will appear in search engines. However, this is not a magic bullet. Traditional methods of getting exposure (like advertising) are much more effective.