This is my super basic guide for people who have never oil painted, and want to try it without spending a fortune.
What is oil paint?
It's just pigment in oil. Oil acts as the pigment binder, the pigment particles act as the color. The pigments get milled with the oil, some extra dryers or fillers might be added, but oil paint is not complex unlike acrylics. The oil used is usually linseed or safflower oil. The pigment is by far the most costly part in oil paint.
Why do people use it instead of Acrylics or Gouache or Watercolor?
Lots of reasons, but mainly because it dries rather slowly, which allows you to create soft edges, wipe off paint, and basically manipulate paint for longer periods of time. Oiil paint is also extremely color rich, it's dense and packed with color particles.
What is "Alla prima"?
Alla Prima means painting in one sitting. It is everything glazing is not. You put paint in your canvas, finish your painting, and let it dry. Alla Prima is popular with outdoor painters, illustrators and people who have a life and don't have time to paint on one painting for weeks ~
Isn't oil paint dangerous, I heard you needed thinners and it's toxic?
No, if oil paint is dangerous depends on your own choices.
You're no longer required to use toxic pigments. You can avoid all cadmium, cobalt and lead based paint (called flake white), and replace them with other colors. You're also not required to use thinners, your oil can act as your thinner, just don't overuse it. Try to find a paint with a good consitency. Regardless, always work in a well ventilated area, even if none of your substances are toxic. Never work in the same area as where you eat. If you're unsure about something, email or call the oil company, and ask them if something is toxic, and how to take safety measures.
What do I need to get started?
Brushes, paint, oils, a canvas, somethign to hold the canvas, a palette, and some cloth
*Brushes. I recommend you buy some flat bristle brushes of varying size. 3 will suit you fine to begin with. Hog bristle brushes will give you the spring you need, make sure you clean them with soap after each session. Be gentle with them, but clean them thouroughly. If they splay after drying, put a tiny bit of soap on them before they start drying, to shape them. I also recommend one smaller round brush for details, a synthetic is fine, you don't need the expensive sabel to start out, and it saves an animal's coat.
*Paint. I recommend this paint: http://www.winsornewton.com/na/discover/resources/colour-charts/winton-oil-colour It's student paint, but really high quality student paint. You'll get access to the best pigments, but at a reasonable price. I would recommend you buy 5 colors. Titanium white, Ivory Black, A middle Yellow (azo works as cadmium alternative), A magenta (quinacridone works), A cyan blue (phthalo blue or ultramarine). Do not start by buying 15+ colors, you do not need 15 colors. Start with 5, then move up to 8 if you need, but don't let the shop tell you you need all colors of the rainbox, you don't. That's what mixing is for.
*Canvas: There are two types of fabrics to paint on, cotton or linen, cotton is cheaper, so I recommend you start with cotton. Cotton canvases come preprimed and stretched for beginners. You don't have to prime your own canvas, you don't have to stretch it, and you never do if you don't want to, many canvases in the shop are ready to be painted on directly.
*Oil will act as your medium. I recommend refined linseed or safflower oil
*Medium / Thinner: Many of them are toxic...so be careful wit them. Like I said above, you do not have to use them or buy them. Oderless thinners are NOT harmless, just because they don't smell, doesn't mean they're not harmful. ALWAYS ventilate your working area when working with mediums or thinnners.
*Some cloth or paper, to clean up, to wipe your brush, some use paper, others cheap pieces of cloth.
*Something to set your canvas up against, this could be an easerl, but could be a desk, could be a wall, anything that works for you.
*A palette for your colors. A palette to mix colors on, this could be in wood, in plastic, in glass, depends on what you like. You don't even have to buy a palette if you don't want to, you can just throw paint from the tube onto the canvas and mix on that, later your can cut to frame. I do this a lot, it's lazy, more costly, but more fun.
*A painting knife. This is optional. A painting knife is used to mix colors, and to create special effects on your canvas. You don't have to use them, I rarely do, you can mix with your brush just fine. It's another choice, I recommend you buy one just so you know what it's like, how it handles and how it feels to mix. But like I said, you don't have to use one.
There you go, have fun.