If statement Help

[shake]

i am trying to make this code when after some one logs in it will say something like Welcome (username) You have (amount of messages) and then a link to the inbox and a log out button i know it a If statement but i am super new to Php So i came here to see if you guys could help.

<div>
<h5>Login</h5>
<form name="login" method="post" action="/fourms/ucp.php?mode=login">
	<span style="font-size:10pt;">Username:</span> <br />
    <input name="username" type="text" value="" size="12" />
	<span style="font-size:10pt;">Password:</span> <br />
    <input name="password" type="password" size="12" /><br />
	<span style="font-size:10pt;">Remember me?</span>
    <input type="checkbox" name="remember" />
	<input type="submit" name="submit" value="Login" />
</form>
</div>

[mlseim]

This involves using PHP SESSIONS to check the user/pass for validity and then
setting the SESSION so they remain logged-in until they close their browser or
log off.

Too much to describe here, but use Google to find tutorials ...
Like this one:
http://devzone.zend.com/article/646