Have a read through Chapter 14 of John Palmers book. Specifically page 14.5, the last paragraph at the bottom.
Have a read through the excellent articles on the US site Brewery.org
The links to these sites are found by clicking on the word link, right near the top of the screen, just under the aussiehomebrewer banner.
There are many other basic mash articles floating around on the internet.
Selection of the malt bill, mash temperature, mash chemistry and grain:water ratios are all tools that all grainers use to tailor a wort to brew a specific style of beer. It is this control of the process that allows all grainers to make a huge range of beers. Kit brewers are limited to light, amber and black malts and some specialty grain steeping.