Apes use tools. So what? What does that tell us about human evolution? As it turns out, observing our closest living relatives as they wield stone hammers and manipulate gadgets can show us how early humans may have been using artifacts. It may even hold the key to the origins of culture, but too much extrapolation in this direction leads to vehement debate within the field of primatology.
Chimpanzees in Ivory Coast's Tai National Park use stone hammers to exert the 1100 kg of force needed to crack open panda nuts, according to a 2002 Science study published by archaeologist Julio Mercader. The chimps find the stones, carry them to processing stations, lay the nut on an anvil and crack it. Chimps have been observed cracking 100 nuts a day, wearing down the stone hammers with pitting and flaking.
By excavating an abandoned nut-cracking area, Mercader was able to compare the chimps' accidentally produced flakes with Oldowan flakes produced by hominins. Their similarities suggest that the earliest hominins could have been using the same technology to eat hard objects. But more importantly, the flake by-products of percussive nut-cracking action could have become the first cutting tools.
It's actually a more extended discussion of possible cultural transmission among chimps, independent invention, etc. Seems more promising to use modern ape behavior to investigate these sorts of cultural transmission issues than to try to figure out what Oldowan tools were used for (equifinality and all that).