I started watching My Hero Academia as an anime, and finished the first season. But now I want to switch to reading the manga instead. Which volume should I start reading from?
According to the BNHA wiki for Season 1 of the anime and Chapter 21 of the manga, since Season 1 has 13 episodes, Season 2 starts with episode 14, and Page 18 of Chapter 21 is where episode 14 starts from.
Therefore, you should probably start reading from Chapter 21, or if you don't care about skipping the one page, you can just start at Chapter 22.
Volume 3 starts with Chapter 18, so you can start there too.