The download of phantomjs through cygwin failed multiple times. If you encounter this error, download the zip-file yourself (your url might vary, depending on your OS), and copy it to the path specified next to "Saving to".
Re-run the npm-command, and the zip-file should be used, and extracted to the correct folder.
Bower is used to manage CSS and JavaScript dependencies. You can upgrade dependencies by specifying a newer version in file `bower.json`. You can also run `bower update` and `bower install` to manage dependencies.
Add the `-h` flag on any command to see how you can use it. For example, `bower update -h`.