Where did you get Thunderbird from ? It's available in the Ubuntu
Software Centre ( under 'Applications' ) and generally that's the
first place to look for software - there's a simple 'Install' button
to make the process quick and painless

Once installed, Thunderbird appears in [ Applications / Internet ] and
the icon can be dragged up to the top bar to create a quick launch.

Note that the programs in the USC may not be the very latest ones but
have been checked that they won't break other programs. Installing
manually from other sources has the potential to break things if you
aren't careful - not that Thunderbird *should* do that, but worthwhile
being aware of as a new user :-)

There's always a trade-off between being cutting edge and stability in
any OS, not just Ubuntu, and is partly why the USC exists !