How I connect SSRS report by using webconfig Connection Str (instead of Datasource)

Hi,

Im a beginner at SSRS reports, I have designed SSRS report by using DataSource + DataSet I can able to view well. I would like to publish the same SSRS report on my aspx web application page, by usingweb.config Connection String, how I connect this to the server? 

Possible pls share some examples (Step by step, how to do) 

Thanks in advance.