OK. Last time. ..
Picture this...Your eyes are like a round ball filled up with gel-like substance.
Before you're born, there is a blood vessel starting from the posterior of your eyes to the anterior of your eyes. Its function at this time is nourished the anterior.
After you're born, the anterior is no longer needed this vessel; therefore, it breaks off into different shaped, sized debris, such as a dot, a cobweb, a string, etc.... Remember, these, even broken up, are still in your eyes.
In general, younger people don't see these debris as much because either:
1. They don't know how to look for them
2. These are settled to the bottom of the eye.
As you get older, the gel-like substance turns into liquid-like substance. So these debris move more freely, hence, you have more chance to see them regularly.
Of course, these are called Floaters, and it's a normal occurance to us mortal human.
It's easy to ID them. When seeing these floaters, as you move your eyes whatever the direction, they "follow".
Now, an advice: If you're suddenly "see" a bunch of debris, aka...like snowing/shower-appearance debris, instead of couple/several here and there, then you need to have eyes checked ASAP.