Differential geometry is divided into classical differential geometry, which focuses on curves and surfaces in Euclidean space, and the abstract theory of manifolds. It is recommended to start with classical differential geometry to appreciate its beauty, learning concepts like Theorema Egregium and the Gauss-Bonnet theorem. Key textbooks include Do Carmo for classical geometry, Pressley for a more elementary approach, and O'Neill for modern treatments using differential forms. Resources such as online texts and books by authors like Jeffrey Weeks and John M. Lee are also suggested for a contemporary understanding. Differential geometry has practical applications, including in mechanics of shells, and some recommend books that include computational algorithms for hands-on learning.