You can buy them online. I buy from my local brew shop and have never bought on line but people swear by northern brewer.
What you should do. (I hate the word "should" but....) What you should do is buy an "ingredient kit". This is a set of ingredients and instructions for a specific recipe. The ingredients usually include (if its an extract recipe): an amount of LME, an amount of DME, some ground specialty grains, pre-measured amounts of the different types of hops you will need, yeast, and priming sugar. The are a *huge* step up from "instant beer in a can" but a large step lower from writing your own shopping list.
If you want to try all-grain, you can get one-gallon or five gallon all-grain ingredient kits from Brooklyn Brew Shop and these are rather easy to use. (Well, the one gallon kits are. 5-gallon all grain is only difficult in that the equipment to do such a size is a bit unwieldy.)
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To give you an example of what I'm talking about here is the second beer I ever did. (The first was a Mr. Beer pre-hopped American Classic which I felt, like you, was kind of hands off.) This is a plug for my local brew shop which has been very good to me. (Don't know how they are online though.)
Shameless plug. There are other places to get kits including some where you can indicate whether you want dry or liquid yeast.
.... and here's a google on "
home brew ingredient kits" so you can see you really have a *lot* of options.