Answer 1

You mean: how to upload an image from the user?
If it is, you not only need html and js ( css is accessory here ), but to code on the server side... So, with which language you want code it? Php is the more frequently used, but you can choice any ( there's web servers framework for almost od the language -- scripting is more comfortable, because they don't have the compilation step: java is an intermediate one, in sense that semi-compile )

The principle is to have an html form with an <input type="file"> tag ( a special field, where you can add attribute "multiple" about selection ) and a <input type="submit"> one ( a special button ):

<form method="post" action="my_upload_script.php" enctype="multipart/form-data">
<input type="file" multiple> <!-- multiple if you want providing multiple file selection/upload at once -->
<input type="submit" value="UPLOAD!">
</form>

In the action attribute of the forme, the url ( absolute or relative ) of your script uploader ( form handler, executing on the server )... but you must googling tutorials and examples on internet, since it takes much more than a post to be adequately covered :P