The needs of any given charity are vast and varied, to put it mildly. While many different charities need similar things, and there are really only three things that you can ever provide to them (your time, talents and treasure), there is a whole lot more to it than just giving blindly and hoping that what you give will help someone. After all, for most people there is nothing more troubling than watching another person go through a terrible situation, knowing that you could easily help them out but not doing so.
Simply put, the charity that you are talking to needs the exact same things that the people they serve need. If your charity of choice helps people to build houses, they need the work of contractors (especially highly skilled people), and they need money for materials. If you have the power to donate either of these things, then doing so would be a very kindly way of showing some support to those who are less fortunate than you are.
However, there are other kinds of organizations which require more of one thing than the other two. A soup kitchen is likely going to need more time, followed by more treasure to be donated to its operation if it wants to be as effective as humanly possible. But on the other hand, a relief effort which is taking place on the other side of the world is most likely going to need treasure, then talents, and then time.