We have had a Close look at how SCCM can be used to request Softwares by Users here :
In this Post we will have a look at the workflow which is being used While a user request for a Software . The below diagram will be more clear to people who have Used MS Visio as the symbols / Images have specific meaning .

Clearly you can see that the SCCM Admin creates the Application in the SCCM Console . User Requests for the Software Using Software Center . User Submits the request . The request goes to SCCM Admin who then approves or rejects the request basis which a decision is taken .