When you open the app on your tablet or mobile device, be sure to choose the languages you want to translate to and from at the top of the screen. Mine, for example, will be English to Spanish.
You will see a camera icon in the upper left corner. Click this icon, and point it directly at the words or phrases you are looking to translate. It will translate it for you right there on the screen.
The process will look a little something like this:
Disclaimer: These translations are often not perfect, so make sure not to rely heavily on this app for all of your translating needs.