You can edit the menu by right clicking on the Ubuntu icon (top left of the
screen) and choose Edit Menus from the drop down. If for some reason the top
panel is missing you can add to the bottom panel by right clicking on the
panel and choose Add to Panel. The "Start" button is called the Main Menu in
the choices of things to add. You can remove the top panel entirely (Remove
Panel) and add icons to the bottom panel, including a "Start" button, so
that it works more like Windows. You can also add a panel (New Panel) if one
is missing. You can have them on any or all sides of the screen. Typicaly
you have to right-click on a blank area of the panel otherwise the choices
change and are for that panel item only.

Not all Linux distributions work the same way, but all can be changed to
suit your purposes. The GNOME desktop environment which is used by Ubuntu
typically has two panels with the main one at the top. I remove the bottom
one to save desktop space. Linux Mint, a distribution based on Ubuntu, uses
only one panel at the bottom in GNOME, so that Windows users feel more at
home. KDE which is another desktop environment entirely has one default
panel at the bottom. I move it to the top so that I can put the Avant Window
Navigator panel at the bottom so it look more like a Mac. The bottom line is
that Linux is very configurable because unlike Windows it is not locked down
and is open sourced. Microsoft wants a universal look and feel which is
understandable since it is proprietary.

If you are still confused, please ask more questions. The users here are
great and very helpful. No question is too dumb and we all started out in
your situation at some point in the past.