In OS X you don’t have a [visible] ../etc/hosts file to edit so you’ll [either need to use pico within the terminal, unhide your files or] use NetInfo Manager which is in your Utilities folder. To add a host entry, you have to click on the category labeled ‘machines’ which will then display a list of the know hosts for your computer. The easiest thing to do is to make a copy of an existing entry and then modify the name and IP address for the copy to match that of the host you’re trying to add.