how to make levels in revit architecture?

You have to select the elevations section in the left toolbar. I don't believe that you can have no levels as everything likes to constrain to a level. Once you know how it takes only a few seconds to set up the levels. This video might help a bit more. http://www.youtube.com/watch?v=6lQYCycfZDg

you should open one of the elevation in project browser
then pick the level tool in architecture palet
now you can add levels by draw a line (with 2 selected point) and set elevation by typping