Need some help with Web User Controls (*.ascx)

Question

I need some help with web user controls. In my site I have created a few Web User Controls (ascx). My problem is that I want to load one or more of these controls at runtime on an aspx web page. I tried many ways but I was unable to find a solution. So I began asking myself if what I want can be done. I need a solution, advice something. Thanks in advance.