I sketched a closed shape (rectangular with a notch cut out), finished the sketch, and performed a revolve. I select the profile and the axis and the solid is displayed. The only revolve type that is allowed is a 'cut', however there aren't any intersecting objects that I'm aware of; it's out in the middle of apparently empty space. When I select OK I get an error message - "Create Revolved Feature: problems encountered while executing this command." The error window has buttons for Edit and Cancel. What am I doing wrong ???
From your screen shot it looks like you are in an assembly file. In assembly mode only subtractive modifications can be performed on parts. So the revolve commad is only allowing cut because it is trying to modify participant parts in the assembly. To make a new part, first use the "create" command on the assemble tab to make a new part, or to edit an exisiting part in place, right click it in the browser window and hit edit.
As Arnie mentioned, you are doing all your work in Assembly mode.
There are a lot of tutorials out there, JMATHER has plenty, I would have a look at his web site for some interesting information.
The reason why it did not work for a second time was that you probably clicked on the Drum Sub-Assembly and not the Part within the sub-assembly.
How I tought myself was to think of the manufacture process, all parts are manufactured indiviually with all features created, then the individual parts are Assembled together via bolts, welds etc. Any work done in assembly mode is carried out on the finished item, which is naturally the removal of material.