The Teacher provides his own commentary of the poem in these verses.
The poem points out that life is an endless round of common activities. These activities keep us busy but offer no substantial or fulfilling gain for humans. All those wonderful activities are merely things to keep us busy, much like the busy work given to us by substitute teachers in school.
Verse 11 is another famous verse. I would suggest you do some extensive research on the ways this verse has been interpreted before making your conclusion about its meaning.
The desire to know the past and the future is a part of the human condition, but we still can’t comprehend why God does what He does. Everything has a beauty that is unique that leads us to contemplate the eternal, if we will only search for it.