If you have performend a RHEL 7 Linux Server installation and did not include Graphical User Interface (GUI) you can do it later directly from command line using yum command and selecting an appropriate installation group. To list all available installation groups on Redhat 7 Linux use:
[root@rhel7 ~]# yum group list
Loaded plugins: product-id, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
There is no installed groups file.
Maybe run: yum groups mark convert (see man yum)
Available environment groups:
   Minimal Install
   Infrastructure Server
   File and Print Server
   Basic Web Server
   Virtualization Host
   Server with GUI
Available Groups:
   Compatibility Libraries
   Console Internet Tools
   Development Tools
   Graphical Administration Tools
   Legacy UNIX Compatibility
   Scientific Support
   Security Tools
   Smart Card Support
   System Administration Tools
   System Management

From the above list select Server with GUI installation group:
[root@rhel7 ~]# yum groupinstall 'Server with GUI'
Transaction Summary
Install  261 Packages (+604 Dependent packages)

Total download size: 527 M
Installed size: 1.7 G
Is this ok [y/d/N]: 
Just because gnome desktop environment is a default GUI on RHEL 7 linux system the above command will install gnome. Alternatively, you can run the below command to only install core GNOME packages:
[root@rhel7 ~]# yum groupinstall 'X Window System' 'GNOME'
Once the installation is finished, you need to change system's runlevel to runlevel 5. Changing runlevel on RHEL 7 is done by use of systemctl command. The below command will change runlevel from runlevel 3 to runelevel 5 on RHEL 7:
[root@rhel7 ~]# systemctl set-default graphical.target
Depending on your previous installations you may need to accept Redhat License after you reboot your system. Once you boot to your system you can check GNOME version using:
[root@rhel7 ~]# gnome-shell --version
GNOME Shell 3.8.4
install Gnome GUI on Redhat linux 7