Hello and welcome!
First question would probably be... Are you going to play, or just build and paint?
If the latter, then you won't need to buy any rule books, army books, dice etc, and also won't need to stick to collecting a particular army - all you will need is sufficient tools to build, and sufficient paints to paint.
As a bare minimum, something like:
A pair of sharp and smallish-tipped side cutters for cutting model parts from sprues
A craft / hobby knife (X-Acto for example) for smaller parts, scraping off mold lines etc
Plastic glue for plastic models
Superglue for resin / metal models
A couple of decent paint brushes of different sizes - suggest starting with a size 0, a 1 and a 2.
Primer (spray can - black / white / grey depending on what you want to paint)
Enough paints to paint what you want to paint in the colours you want to paint it - intentionally vague...
The
GW Paint smartphone app is actually pretty good and well worth a look through. It includes paint scheme suggestions for most armies, tips on techniques and a lot of links to the Warhammer TV videos on YouTube, which are also a fantastic resource and go all the way from getting started to producing some great looking models.
For starting out painting, the first thing to focus on is just applying paint neatly. The
GW paints are a little thick straight out of the pot, so thin them down slightly with some water. It's generally considered better to apply 2 thin coats rather than 1 thick coat. If you slap the paint on too thickly you will obscure the details of the model.
If you are intending to play as well, then the first thing I'd recommend you do is visit one of your local stores and play an introductory game. The guys running the store should offer this as a service. Will at least make sure it's something you enjoy before you spend anything.
After that, pretty much same as the above but you'll be needing some rules as well, and you'll be looking at collecting and building a viable army to play with. There are rule books for building each army, what the different troops are, how many points they cost and so on.
A new version of the game came out about a year ago, and they are still writing rule books for all the armies - I think they've done about two thirds of them now. Old books aren't compatible with the new version of the game, so don't be suckered into thinking you've got a bargain with buying an old book.
Oh, and you'll also need a load of 6 sided dice.