Pete's right. Unzip or untar the downloaded bundle - as you're in the UK get the UK mod bundle, too and load them at the same time. But look in the untarred folder first. There is a directory/folder called in there called docs. Inside there are some .html files, including 0.about_zen_cart.html and 1.installation.html - open each in a browser and have a read through before you do anything else. You could look through a couple of the others, too, but you don't have to at this stage.
You can get the UK module, so default language becomes English English instead of American English, currency ŁUK, weight kg and so forth, here:
Mutual Advantage and there is tons of help and assistance on the
Zen Cart forums, to which I am an occasional visitor, helping sometimes and asking questions at others.
But then, as Pete says, you could get him to do the installation part for you.
zen cart
Linear Mode
December 2008
