Create file
vi /etc/yum.repos.d/mongodb-org-4.0.repo
Add
[mongodb-org-4.0] name=MongoDB Repository baseurl=https://repo.mongodb.org/yum/redhat/$releasever/mongodb-org/testing/x86_64/ gpgcheck=1 enabled=1 gpgkey=https://www.mongodb.org/static/pgp/server-4.0.asc
Install MongoDB with
yum install -y mongodb-org
Set MongoDB to start on boot.
chkconfig mongod on
Start MongoDB
service mongod start