You can install gem with a single command at the command line:
The following command installs feedtools
gem install feedtools
If all goes well, you'll get output like this:
Successfully installed feedtools-0.2.29 Successfully installed activesupport-2.3.0 2 gems installed Installing ri documentation for feedtools-0.2.29...
First, RubyGems looks to see if the gem exists in the current directory, and if not, it goes to RubyForge to download the gem and install it.
In many cases, installing one gem requires other gems to be installed too.
If this is the case, RubyGems will tell you, and will install the required gems in each case if you agree.