I am using a raspberry pi 2 model b running raspbian wheezy. I am trying to install a package
autoconf and it says:
$sudo apt-get install autoconf
E: no such package autoconf
That message means that apt can't find autoconf in it's package lists. The package definately exists in the raspbian repositories so it seems like you have some kind of local problem.
First if you have not run "sudo apt-get update" do so and then try the install again.
If apt-get update gives errors post them so we can advise further. If apt-get update succeeds without any errors but the apt-get install still fails then post the contents of /etc/apt/sources.list