When you submit a form using the GET method form values will appear in the url.
http://localhost/form.php?name=Mr+Smith&age=101&submit=submit
GET /form.php?name=Mr+Smith&age=101&submit=submit HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.0.5) Gecko/2008120122 Firefox/3.0.5 (.NET CLR 3.5.30729)
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-gb,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive
Referer: http://localhost/form.php
With the POST method the form values get sent in the body of request and therefore not shown in the url.
http://localhost/form.php
POST /form.php HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.0.5) Gecko/2008120122 Firefox/3.0.5 (.NET CLR 3.5.30729)
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-gb,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive
Referer: http://localhost/form.php
Content-Type: application/x-www-form-urlencoded
Content-Length: 35
name=Mr+Smith&age=101&submit=submit