I am a beginner of first-order logic and this is one of the first books I've read about it, although the book also introduces and explains some other famous topics and theorems too so the book introduces the reader to a lot of new things in the field with many book recommendations.
I'm not accustomed to reading first-order logic and maths either, and the author's explanations and writing style could be clearer and in a better format, because of this I wouldn't recommend the book to someone who quickly needs to understand the way first-order logic works but rather someone who is familiar with it but wants to deepen their knowledge of it at a beginner-low intermediate level.
If you want a short book that is high on detail on the subjects of truth trees, propositional languages and first-order logic then this is certainly one to read.