Here's how I do it, step by step:
1. I tap on the folder labelled 'Google'.
2. I tap on the icon labelled 'Maps'.
3. I tap in the 'Search here' field.
4. I type in the location that I want to go to. (The postcode is easiest but a street name or, say, the name of a visitor attraction should also work).
5. I tap the 'Search' button (= the magnifying glass one).
6. The map then shows my destination. At the bottom of the screen there's a panel with buttons for 'Directions', 'Start', Save' and Share. I then simply tap on 'Start'.
NB: Tapping on the map toggles that bottom panel on and off. If you're not seeing it, try tapping the map to see if that will then bring it up, so that you can use it.
3.