Jenkins is nice CI tool and is easy to install and setup it. Below are steps for CentOS 7, assuming you have already Centos 7 installed and able to connect to internet, do below in order to get Jenkins server installed and running
Get Jenkins repository information and upload key
wget -O /etc/yum.repos.d/jenkins.repo http://pkg.jenkins-ci.org/redhat-stable/jenkins.repo rpm --import https://jenkins-ci.org/redhat/jenkins-ci.org.key
Install packages and open Jenkings port
yum install java-1.7.0-openjdk systemctl start jenkins systemctl enable jenkins firewall-cmd --zone=public --add-port=8080/tcp --permanent firewall-cmd --zone=public --add-service=http --permanent firewall-cmd --reload
After this you can access jenkins web interface via http://server_hostname:8080, where server_hostname should be $(hostname -s).
Further tweaking might be directed toward Manage Jenkins -> and pick up what you want to change. Installing some plugins – like git ones related can be helpful. rpm -ql jenkins will give list of files which are part of jenkins package installed in step above from where you can investigate it further – and eventually change some default parameters ( check /etc/sysconfig/jenkins for details )