A good introduction to qubits for non-specialists, by the person who coined the word, is found in Lecture 21 of ‘‘The science of information: from language to black holes’’, by Professor Benjamin Schumacher,The Great Courses, The Teaching Company (4DVDs, 2015)。
A picture-bo͘k introduction to entanglement, contrasting classical systems and a Bell state, is found in “Quantum entanglement for babies“, by Chris Ferrie (2017)。