Where does the blood go?
Let's say you just went to donate blood.
That blood goes through checking and filtering to make sure it isn't contaminated.
Then, it is sent to a blood bank, maybe hospitals, who knows?
It can be used during surgeries, or for people who lose blood frequently, etc.
Oh, besides, it can be used overseas to help the soldiers!
That's just a few ways donated blood can be put to use, but there are many, many more.