You can also enable the feature using an Administrative command prompt, useful for keeping a script around to easily add features needed on the fly.
For example here is how to enable Telnet:
dism /online /Enable-Feature /FeatureName:TelnetClient
Deployment Image Servicing and Management tool
Image Version: 6.3.9600.16384
The operation completed successfully.
To see the names of features to be able to script others, issue the "dism /online /get-features" command.