In this colloquium, I am going to mainly talk on my recent work on the tidal disruption of stars by supermassive black holes, specifically how accretion disks are formed around spinning supermassive black holes in tidal disruption events. Since I am moving from KASI to CBNU soon, I would also like to talk on how to find evidences for binary supermassive black holes on sub-parsec scales in the context of the binary-disk interaction, which is another topic I have been working on with colleagues in KASI.