There are two or three rows of feathers that are different lengths. (Click for larger image.)

Why are they different? What do they do?

Answer:

• The longest feathers are the flight feathers. The ones closest to the wing tip are primaries. As they flap, they help the bird move forward. The secondaries, which are closer to body, give more lift.
  
  
• The softer medium-size feathers, called coverts, overlap the flight feathers. Along with the short feathers (called lesser coverts), they keep the bird flying well. They form a smooth area that air flows over. This lifts the robin and holds it up. They also protect the wing and tail feathers.

The feathers have a thing like a straw in the middle.

How does it feel? Why is it there?

Answer: It (the shaft) feels stiff. It makes the feather strong enough to beat a million times during the year the bird has it.

The shaft isn't really in the middle. The sides of the feathers are not equal.

Why aren't the sides of the feathers equal?

Answer: The narrow side is the leading edge. It needs to be stiff and strong to slice through the air. The wide trailing edge gives the feather more surface area. When the wing flaps downward, these large surfaces push against the air to hold the bird up. Learn more about how birds fly.

The feathers are not all the same. The tips of the front ones are more pointed. The tips of the back ones are more rounded.

Why do the feathers have different types of tips?

Answer: The front feathers must slice through the air; the pointy tips help them do this. The broader feathers in back have more surface area to hold the bird up.