rpm -Uvh https://yum.postgresql.org/11/redhat/rhel-7-x86_64/pgdg-redhat-repo-latest.noarch.rpm
yum -y install postgresql11-server
/usr/pgsql-11/bin/postgresql-11-setup initdb
systemctl enable postgresql-11.service
systemctl start postgresql-11.service
Test:
su - postgres -c "psql"