which technology is better to upload files to site?

Please see my comment to the question. Chris is absolutely right. It's pretty hard to explain everything from the very beginning, because from the very beginning it could take a whole article for the absolute beginners you might really need. So I'll just give you a basic hint.

To start with: you need both client side and server side to transfer a file from a client to a server. On a client side, you need just an HTML form with the method "post" to send an HTTP request to the server. This request will contain the full content of the file to be uploaded. The server side needs to read the post and do something with the data sent over the HTTP protocol, for example — write the file(s). On the client side, you can also perform the post using AJAX, and here you may or may use jQuery. Usually, a form without any client-side scripting would do just fine.

On the server side, you need some server-side code the process the data as I explained above. Here comes the choice between the server-side technologies: PHP, ASP.NET, Python with WSGI, etc. — you name it. Even here, the predicate "better" is not defined — it depends.

—SA