How to map DS to infosource

Hello

How do u map a datasource to infosource? I mean say i have reporting req which used sales cube 0SD_03.Now How do i know that I have to map 0SD_03 to XYZ infosource?

There are so many standard infosources available with Business Content.How do i know that i have to map the DS to one of those std infosources or I have to create infosource and then map 0SD_03?

Please guide me.I am really confused about this.I am not sure how to map the DS to std infosource or to a custom infosource which i have created.If someone can tell me step by step method or forward me a document regarding the same?(except for help.sap.com), i wud be helpful.

jackson_carvalho@yahoo.com is the id

Thanks