<form id="uploadbanner" enctype="multipart/form-data" method="post" action="#">
<input id="fileupload" name="myfile" type="file" />
<input type="submit" value="submit" id="submit" />
</form>
To upload a file, it is essential to set enctype="multipart/form-data" on your form
You need that form type and then some php to process the file :)
You should probably check out Uploadify if you want something very customisable out of the box.