Extract kits are almost fool proof...the water chemistry comes with the extract...making your own recipes (for either ag but more to the point extract) is a little more difficult...but can be picked up with a little experience...it's just like cooking...look at enough recipes, and play with the software and you will understand the variable that go into it...
ANd then the rest is up to you...you can be impatient, not use temp control or your hydrometer, cut corners on your sanitization ..that will determing whether or not the beer will turn out.
But to start out, doing a couple of kits will get your feet wet, without a lot of extra things to worry about.
As to where to buy, there are a ton of threads on here...this one looks to have several links
Welcome to the obsession!