For starters, we need to have an understanding what castling is and what it looks like on the chess board. Castling is a move that involves your king and either of your original rooks “the castle looking one”. It is the only move in chess in which a player moves two pieces in the same move, and it is the only move aside from the knight’s move where a piece can be said to “jump over” another. On one more side note, castling is also the only move in which your king is allowed to move two spaces.
The king and rook may not have moved from their starting squares
All spaces between the king and rook must be empty
The king cannot be in Check
The squares the king will pass over may not be under attack, nor can the square on which the king will land