If we humans evolved from apes,
Why on earth are there living apes?

Because we specialised differently from them. Their evolutionary line was just as viable as ours- that's why they still exist. Look at it another way- if apes evolved from bacteria, why are there still bacteria? The answer is simple- because they can find something to live on. And the first eukaryotes that evolved from bacteria* could also find something to live on, so they survived (until they died out, but not before they'd evolved into the something else that eventially evolved into the next thing that.... led to apes).

Get over the idea that evolution is a linear thing, that it's going somewhere. It certainly WENT somewhere, but that's another thing entirely.

* Actually, it's probably truer to say that bacteria and eukaryotes (i=ncluding apes and people) shared a common ancestor. DNA analysis is throwing up some remarkable results, including that many assumtions about lineages are being challenged.