Tracking

When I downloaded the add-ons Collusion and Ghostery, I found that several people were tracking me. I went to several different websites such as Facebook, Pinterest, Youtube, and I googled some things. On Facebook and Pinterest and Youtube I had only a few trackers at a time. However, when I googled something I ended up with 22 trackers at one time. I do not fully understand the purpose of tracking but I do find it scary. I am definitely going to be more careful and aware of these things when I use the internet.