Think of the finger build as having two parts. You will build four fingers and four tendons. The fingers are a straw tube with cuts to allow joint movement and retain enough material to bounce back into shape. The tendons consist of a finger nail, tendon, and pull ring. The tendons are one straw piece each and are the secret-sauce to the finger working properly.
All four straw fingers can be made identically. If you wish, you can make the knuckle locations in proportion to a real hand with various lengths. That simply adds more complexity to the build.
You will notice that each finger consists of seven paper punches. You will make four equally spaced paper punches at the bottom of each finger. These will later allow us to create a palm to hold the fingers together. The three punches you make above the palm are at 90 degrees to the palm punches. These are the knuckles and you can hold a straw up to your hand to determine the best location for these punches.
The knuckles require a bit more work to function. You need to remove half of the straw below the hold punch. You can either use scissors to make a nice V shape or just double punch offset below the first. After a lot of experimenting, I think the V shape is both faster and gives a superior 'bounce' for returning the finger to its resting position. Play around with the knuckles by flexing the finger to check for a nice easy bend. Look for plastic crimping and remove that material. The finger should snap back to a straight line when released. If not, you removed too much material.
We will build the opposable thumb as separate series of steps later in this guide.