When you search for directions on a map, on the bottom panel (where it shows you the estimated time and distance for your trip), you'll see a "START" button with an arrow. That's the Navigation button. Start that and, as long as you're using GPS for location services, it'll fire up Turn-by-Turn Voice Guidance. Should you want to mute the virtual gal telling you what to do as you drive/walk/ride, just tap the menu button (or the three dots on the right of the bottom panel) and select "MUTE VOICE GUIDANCE".