Start with The Story of Art for chronological and stylistic orientation, then use Art History: A Very Short Introduction to understand how the discipline frames evidence and interpretation.
For close looking, Smarthistory is useful because it is built around visual description and contextual explanation. The National Gallery gives museum-led talks centred on major paintings, while The Museum of Modern Art is stronger for modern and contemporary art, curatorial practice and artist interviews.
For method, Ways of Seeing helps you think about looking, gender, ownership and reproduction, and Methods & Theories of Art History gives a bridge from description to theories of interpretation.
For current debates, The Week in Art connects art history with institutions, exhibitions and art-world news, while Bow Down broadens the canon through focused episodes on women artists.
If you want structured online study, Modern Art & Ideas links modern art to themes and objects, and Stories of Art develops visual and historical understanding through National Gallery paintings.