Likely the best resource to learn about philosophy is the Stanford Encyclopedia of Philosophy [0]. It's meant to provide a rigorous starting point for learning about a topic, where 1. you won't get bogged down in a giant tome on your first approach and 2. you have references for further reader.

Obviously, the SEP isn't perfect, but it's a great place to start. There's also the Internet Encyclopedia of Philosophy [1]; however, I find its articles to be more hit or miss.

[0] https://plato.stanford.edu

[1] https://iep.utm.edu