When I try and install a package with apt-get, I get the error message:
E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable)
You can't have two package installers open at the same time. For example, if you have the Synaptic Package Manager running and attempt to install a package using apt-get you will receive this message. This is true even if Synaptic is simply open and doing nothing else.
Shutdown Synaptic and then retry the apt-get command.