I've been given Gravitational Waves: Theory and Experiments Volume I to read for a project. The problem is, I haven't learned General Relativity to a high enough level and the book is proving very difficult for me. The book dives straight into linearised gravity in the first chapter, and the field-theoretical approach to GR in the second chapter. Can anyone give me some recommended reading to help bring me up to the necessary level to understand this book? Thanks in advance for any replies.