Docker provides instructions for how to install Docker on CentOS7: https://docs.docker.com/installation/centos/
Roughly:
curl -O -sSL https://get.docker.com/rpm/1.7.0/centos-7/RPMS/x86_64/docker-engine-1.7.0-1.el7.centos.x86_64.rpm
yum localinstall --nogpgcheck docker-engine-1.7.0-1.el6.x86_64.rpm
service docker start
Then to test:
docker run hello-world