You can track the outcomes of closed opportunities and produce reports on them.

To close an opportunity,  select Close Ofin that opportunity's detail.  

Enter the details relating to whether the outcome was Won, Lost or No Sale. Add a reason for the outcome as this information is important for addressing future sales. The information is useful to sales managers when working with their reps. 

when you have completed entering the details.

The result will be reflected on the opportunity details, The opportunity will display as closed, with the outcome and reason for outcome displayed

You will also notice that the Actions menu will display a Re-Activate option. This will reverse the close off action you performed