One of the common questions on beginning woodworking forums is how and where to buy wood, and often enough what wood to buy. There are quite a few places to buy wood, including national retail chains, chain lumber yards, and local mom and pop operations. Of the three, I nearly always recommend using the local mom and pop. This isn't some Norman Rockwell nostalgia thing, but a matter of experience.
For a lot of people just getting started in woodworking, the national home center chains provide a certain level of comfort. They're known brands, they present a familiar retail experience, and you can browse at your leisure. They've also got everything you need to build basic projects, even if you're starting from nothing. They have a large selection of tools, wood, fasteners and finishes. You can get it all in one trip (or so you'd like to think). The problem is that the wood they sell is intended for the burn barrel, not building. It tends to be twisted, warped, cupped and generally resembles an interpretive dance of a storm at sea. Don't buy it. It only looks like buying the wood here is going to make your life easier. *Don't do it.*
The national lumber yard chains may or may not have good lumber. I haven't purchased from them, but I have friends in the construction industry who are generally not pleased with the material they deliver. My current house has a one inch difference in the height of the floor from one joist to the next in my kitchen (or did, a few hundred pounds of self-leveling floor compound can work wonders). You can bet the builders (who were not noted for having the slightest clue about how to build a house) purchased the lumber for the entire subdivision at a national lumber yard chain.
I've bought a lot of lumber from the mom and pop lumber yards though. It's by far the best experience. They don't have a national advertising campaign to draw people in, so they need to rely on word of mouth. The only way to do that is good material and good service. I've found that to be true across multiple lumber yards. If you're comfortable with the normal impersonal retail experience, the lumber yard may be a bit uncomfortable. You don't get to wander around the aisles unescorted to browse at your leisure. Instead you walk up to a counter and tell a man what you'd like. You pay him some money, he hands you a sheet of paper, and tells you where to drive your truck. When you get there and hand the guy waiting there, he selects the wood for you, including discarding any warped or damaged pieces and loads it into your truck. The lumber yard hasn't been designed to look pretty, and lord knows the guys working there aren't nicely dressed retail employees. They're hairy, they wear rough clothes, and by the end of the day they probably don't smell that great either. But they're going to make sure you get good materials at a decent price, and they'll make sure you're properly taken care of.
If you're a woman this might be very intimidating, because this is without a doubt guy territory. There's so much testosterone in the air if I go in clean shaven, I come out with a five o'clock shadow. The good news is that guy territory is open to everybody who comes in with good intentions. If you're open and direct, look people in the eye and speak with confidence in your voice (even if it's confidence that you're not sure what you're doing), you'll be welcome there. Especially if you're spending money.
One last item: lumber yards and anybody else who sells lumber has a saw on premesis to cut your material down. Don't give them your cut list and ask them to cut your material to size for you. It will end badly. If you must have your material cut, have it cut to a size to fit in your vehicle, but no more.