From the Go menu in Finder, select Go To Folder... (or just press Command + Shift + G) , type in /private/etc and then hit Return. The hosts file is there.
If you're gonna work in the Terminal, just tpye cd /private/etc to reach the directory or if you're gonna edit it with a command line-based text editing tool like pico, nano or vi you can simply type:
$ sudo pico /private/etc/hosts
or
$ sudo vi /private/etc/hosts
or
$ sudo nano /private/etc/hosts
