Cmd+tab is like the task switcher in Windows, except it only pulls the menu bar up for the application, and not the application itself.
Q: How do I switch between applications such that the application is visible?
The application switching process is nearly the same as on Windows (& step 5 is optional :-):
If you're asking what I think you're asking, cmd+` will usually cycle between application windows within a single application.
It's also possible you have no application windows open, and you're just getting a menu bar.
Also, this should probably be in the superuser stackexchange.