When he was young, Boba enjoyed reading a lot and would often go to check out books from the local library in Tipoca City. Whrr was the local librarian that would check-in and check-out the books. Whrr wasn't the actual name of the librarian but instead the name that Boba gave him/it because of the whrring, clicking sound that it made as it moved around inside. Although he never actually saw Whrr, Boba assumed it was a droid. The two them became friends with one another and would talk about the different subjects that Boba read on. Before having to make a hasty retreat from Kamino -- following the appearance of the Jedi Obi-Wan Kenobi -- Boba ran to the library to return the books he had checked out recently. However, while doin this, Boba didn't realize until later that he had accidentally put the Black Book his father had given him in with the books he was returning.
Following his father's death at the hands of Mace Windu, Whrr showed a kindness to his little friend by not only returning Boba's black book, but giving him some credits as well to help the young Fett on his journey to find Count Dooku.
Source: Boba Fett: The Fight To Survive