Where to put php code?

Hi, I am trying to create a form for wordpress without using plugins but cannot seem to find where to store my php code. I have tried it in the root directory of the web site, the theme root folder , and tried making a template but the page end up being blank. Could anybody tell me where php files should go on wordpress?

My code below:

<form action="account.php" method="post" id="account" name="account"></form>
<fieldset><legend> Account </legend><label for="name">Name:</label>
<input id="name" maxlength="45" name="name" type="text" value="" />
<label for="address">Address:</label>
<input id="address" maxlength="45" name="address" type="text" value="" />
<label for="contact">Contact:</label>
<input id="contact" maxlength="45" name="contact" type="text" value="" />
<label for="phone">Phone:</label>
<input id="phone" maxlength="45" name="phone" type="text" value="" />
<label for="fax">Fax:</label>
<input id="fax" maxlength="45" name="fax" type="text" value="" />
<label for="email">Email:</label>
<input id="email" maxlength="45" name="email" pattern="[^ @]*@[^ @]*" type="email" value="" placeholder="Enter an email address" />

&nbsp;

<label for="hierachy">Hierachy:</label>
<input id="hierachy" maxlength="45" name="hierachy" type="text" value="" />

<input type="submit" value="Save" /></fieldset>