Welcome to LQ!!
One of the very first things to learn on Linux is the Package Manager---it is in your menus somewhere--under the name of Install SW, Install Applications, or something like that. Normally you want to install things using the package manager before trying anything else.
In the case of Thunderbird, it's pretty easy.
Open the terminal**
enter "su" to become root
locate the tar.gz file (probably) in Desktop
move it to /opt
extract using "tar -xzvf filename"
go into the directory that is created
run the thunderbird script
Here are the exact commands, assuming the file is in Desktop, and is named thunderbird.tar.gz (I'll use a wildcard which works as long as there are no files with similar names.)
<<Open the terminal>>
<<enter root password at the prompt>>
mv thun* /opt
tar -xzvf thun*
**Here are some links on where to find the terminal in that particular netbook