This is the same board photographed from one side, then the other. In each case, you can trace the lines of the rings from the end to the surface.
The board was milled from the outer edge of the tree. The arched grain on the surface is called cathedral figure.
This piece of oak is from the center of the tree. The rays are easily seen as they break the surface. The effect is called silver grain.
The growth rings in this piece of softwood show the center of the tree going out to sapwood. Clearly visible is how the end grain gives way to long grain.