These are, for the most part, very basic scripting commands. The first is using parameter substitution to set a default value for the varibles, and > is a redirect to send something to the specified output file. This last line can't stand by itself though, as you posted it. There needs to be something in front of it to redirect first.
* is simply a (globbing) wildcard. It will match any string of characters.
The third is simply a string of commands linked together using | pipes. The output of one command is sent directly into the input of the next.
If you want to learn these things, start going through one of the many good online guides and tutorials. Here are a couple to start you with:
Linuxcommand.org
Bash Guide for Beginners
