This quote in Harper Lee's To Kill a Mockingbird, is a reference to how long it takes Mr. Avery to whittle a piece of wood. The idea here is that someone working with wood would take a long time to do it, and would need to be talented to accomplish such a feat.
Jem and Scout look at the soap figures—that look so like them—and wonder who could have made the dolls. They are made of soap and show a great deal of detail which indicates an enormous amount of talent. They can think of no one who might have done so.
However, this gives the reader new information: if it is, in fact, Boo Radley who is leaving these gifts, he not only cares about the children enough to give them gifts, but he is a talented young man in spite of all the hardship he has experienced. It also makes one wonder what he might have done had his parents handled his teenage "mistake" more compassionately.
When Scout and Jem find the carvings, they ask themselves who they know that whittles, or carves wood. Carving and whittling were common past-times for men in the South, especially those who were unemployed or otherwise had time on their hands. Whittling can be practical, but often was just a form of stress release. Whittling often only involved stripping a piece of wood slowly until there was none left. In the exchange between Jem and Scout, we learn that Mr. Avery starts with a piece of stovewood, and by about the end of the week has "honed it down to a toothpick and chewed it" to pass the time.