A board is considered “quarter-sawn” when the growth rings run, more or less, perpendicular to the face of the board. Quarter-sawn boards generally have straight grain and are less prone to shrinkage, compared to other boards. These factors don’t come into play with the 2x4s you use to frame a closet—but it does with the shelves and cabinetry you put into that closet; you want those boards to remain straight, flat and stable.
While many woods can be used for carving, there are some clear favorites, including Aspen, Basswood, Butternut, Black Walnut, and Oak. Because it has almost no grain and is notably soft, Basswood is particularly popular with beginner carvers. It is used in many lower-cost instruments like guitars and electric basses. Aspen is similarly soft, although slightly harder, and readily available and inexpensive. Butternut has a deeper hue than Basswood and Aspen and has a nice grain that is easy to carve, and thus friendly for beginners. It's also suitable for furniture. While more expensive that Basswood, Aspen, and Butternut, Black Walnut is a popular choice for its rich color and grain. Lastly, Oak is a strong, sturdy, and versatile wood for carving with a defined grain. It's also a popular wood for furniture making.