To find your address, open up a new browser window, go go https://maps.google.com and enter in your exact address and press the Enter key. Once the map is displayed, zoom in our out as you prefer and then look for the icon to show the embed code for the map as you see it on the page. Copy the code and then carefully paste it into our html file.
If it's a wordpress template, most likely there is a page in the wp admin (in the theme's settings page) that allows you to enter in your address, and the API will automatically render the correct map)
If it's an html template, you'll need to look at the source and see what it's doing.
I've seen some html templates where the map is just hard-coded. Meaning they are only there to show how the page would look with a google map, but it's up to you to add the code to get it to work.
I've seen other html templates where the google map is displayed in an iframe. Look at the source code of the page, look for an iframe that includes 'maps.google.com' followed by a long string of code. That is the address. To find your address, open up a new browser window, go go https://maps.google.com and enter in your exact address and press the Enter key. Once the map is displayed, zoom in our out as you prefer and then look for the icon to show the embed code for the map as you see it on the page. Copy the code and then carefully paste it into our html file.
The google documentation will tell you how the google maps API works - but *how* it is implemented in the template you bought - that all depends on the author of the theme. If you purchased the template from themeforest or template monster, both offer support. Since many other people probably bought that template as well, chances are good they have documentation for updating the map.