Geocode is geographic coordinates: latitude and longitude. For example, 48.858254, 2.294861 is coordinates of the Eifell Tower in Paris, -15.849054, -69.326599 is coordinates of the lake Titicaca in South America. 

How to find a geocode of desired object? This is very simple.

Go to Google Maps and find desired object, then make right click and choose "What's here?". You'll see a popup window bottom: 

opencart geocode 

You can copy these coordinates and use them. For example, geocode in OpenCart 2.0 you can enter in System -> Settings. Just put the geocode to geocode field. Pay attention to our Opencart 2 extension Google Map from Geocode.