Login as root and run the following commands:
cd /etc/apt
echo "deb http://http.debian.net/debian wheezy-backports main" > /etc/apt/sources.list.d/backport.list
apt-get update
gpg --keyserver pgpkeys.mit.edu --recv-key 7638D0442B90D010
gpg -a --export 7638D0442B90D010 | apt-key add -
(should get the ‘OK’ as answer)
Installing a single package from backports:
apt-get -t wheezy-backports install {package-name}