"I am thinking about it."
I'll try to help here, but if I'm off someone correct me!
In French, 'y' (also sometimes 'en') stand in place of a previously mentioned thing or place. e.g:
Person 1: "I am going to the cafe, and you? = "Je vais au café, et toi?" Person 2: "Yes, I am going there." = " Oui, J'y vais."
It's a matter of convenience. Of course, in order to fully understand the sentence, it helps to actually have the previous thing or place named, which DuoLingo doesn't provide...you just kinda have to guess.
Hope this helped! (Hope I'm right!)