Understanding (not) how web searches work

In trying to make our website more visible one of the things to consider is how well we appear on organic, or non-paid searches on engines such as google. You'd think this was easy but hey, to a non techo, it is not. Nor is it easy to understand some of the answers you get from people who you would think should know - like the help desk of your web host.
Just take the question of an ordinary search for delphiniums as an example:
If you are in New Zealand and search for delphiniums you get Dowdeswell's Delphiniums at numbers 1 and 2. If however you are in the USA and do the same search, where are we? Not so easy to answer. A few months ago there was a google tool to allow you to search as if you were in the USA and we came up....nowhere in the first 10. I can't find that tool now and wouldn't you know it, didn't do a search while I was in the USA. Google searches do seem to be more regional though and this is something we have to find more about.
I'm just about to email some friends in the USA and England and getting them to do searches for us. I'll let you know the results.

Of course, if there's anyone out there can help, please drop me a line.

Cheers

Terry