Book recommendations regarding agnosticism and religion in general

Hello!

I've been an agnostic theist ever since I changed schools from the Catholic school where I had previously attended. I recently felt the urge to learn about the topic and so I am here to ask what are some books you may suggest to me about agnosticism in order to further my knowledge Friedrich Nietzsche seems like a good starting point based on my research, however I'm worried about the difficulty of the subjects I would be dealing with since I am unfamiliar with him.

Thank you!