Will I be useful?
In your day-to-day work you'll be helping impoverished people. Ultimately, though how useful you are depends on you! The volunteers who are willing to accept that life will be different, and won't always go to plan, are usually the ones who have the most successful placements. Likewise, those who can use their initiative, will both give the most, and in return gain the most from the experience.
Many volunteers choose to undertake additional "side projects" while working. If you see something missing or not working correctly while volunteering, make it your mission to fix it while you're there. It doesn't need to be huge! Maybe it's a leaky tap, a broken gate or a chicken coop that needs to be built. Whatever it is, it will be your legacy after you've left!
There are so many ways to contribute, something that seems very small to you is likely to be life-changing for the person you are helping. A small act of kindness goes a long way.