If you want a good overview of amplification, the options available, with tons of pointers and definitions and explanations of how things work so that you can best figure out the correct solutions to your playing situations then I highly recommend Deborah Henson-Conant’s The Gurls Guide to Amplification.
It isn’t an overly technical or in depth explanation. It is a basic overview, but that will give you a good basic understanding of what different pieces of equipment you might want, what they do and how they are used. You will be able to walk into a music store and know what to ask and be able to understand what the people trying to help you are talking about.
There are more in depth books out there, but the thing about this one is that it deals specifically with harp amplification and so includes some of Deborah’s explanations of harp specific problems she has faced and how she and her sound people have overcome them.