You need to make a palette to squeeze raw paint and mix on. You can use most anything for a palette. Some suggestions:
• Freezer Paper: It's like wax paper, but heavier and paper-white. Wrap it around some kind of flat surface and tape it on the back. Pros: Quick, cheap, disposable. Cons: *glaringly* white (you hafta compensate for that, visually, depending on the color/value of where you're applying the color on your canvas), disposable means you'll be throwing paint away.
• "Thumb" Palettes/classic movie artist things, frequently paired with berets): Those wooden palettes you can buy that have an oblong hole to hook your thumb through so you can hold it. Pros: moveable (!), portable, comfortable, relatively inexpensive. Cons: small, wiggly.
• Long-term, Homemade Palette: If you have dedicated studio space, I recommend this. It's roomy enough to hold lots of raw paint squirts as well as providing ample room to mix colors. Make it as large as you can. (I never seem to have enough room on mine since there's always a trade-off between large size and the restrictions of the size of the table I'm putting it on, and how far I want to stretch to reach its farthest corners. Moderation, moderation!)
Your mixing surface should be flat, uniformly colored, as smooth as possible, and as non-oil absorbing as possible. In general, it's a good idea to have it be somewhere in the 30-60% "gray" range (regardless of color, but try keeping it earthy and/or neutral). Possible materials (I've used them all): Glass, mirrors, plexiglas (opaque gray plexi is great), plywood, masonite. You'll have to experiment and find the best for you. I prefer masonite, though in college I once made a great one out of mahogany plywood.
For a masonite palette (or plywood, or anything potentially absorbent), I prep it like this: I get the size/dimensions that I like, then I impregnate the surface with linseed oil. If you don't do this, when you squeeze paint onto it, the (thirsty) substrate will suck all the linseed oil (oil paint's "vehicle") out of the paint. Sometimes this is desirable--Ed Degas used linseed leeched/starved oils for some of his paintings--but let's not go there now. Get your linseed oil, pour some onto your palette, and rub it al over your palette. You can use paper towels for this. Let it sink in, and do it several times a day for two days. Your first paint squeezes & mixes still might be a bit leech-y, but after using for a couple of days, squeeze some fresh paint. The mixing area will prolly be ok since you'll have mixed on it, then cleaned it several times.
Your palette will become much like a well-used wok or cast iron skillet; the more you use it, the more "seasoned" it will become!