If you are coming from imperative land (more specifically C++) then nothing beats articles and videos by Dr. Bartosz Milewski:
https://bartoszmilewski.com/2014/10/28/category-theory-for-p...
https://www.youtube.com/watch?v=I8LbkfSSR58&list=PLbgaMIhjbm...
https://www.youtube.com/playlist?list=PLbgaMIhjbmElia1eCEZNv...
https://www.youtube.com/playlist?list=PLbgaMIhjbmEn64WVX4B08...