Total depravity asserts that our entire being is involved in sin. Sin is not just a matter of not understanding something. It is basically a derangement of the will, so that we are focussed on ourselves rather than God. Similarly, it shows up in everything we do. This does not mean that everyone spends all their time in rape and pillage.
People are capable of good actions.
However even their best actions are done from motivations that are mixed. There is enough selfishness even in what appear to be good actions that they cannot be accounted by God as righteous. People often say that original sin means somehow children are held accountable for someone else's sin, because they haven't had a chance to do any of their own. I hope you can see from my explanation above that this is false. Original sin isn't a specific action.