Preparing flour involves sifting it, which is the process of passing it through a sieve or other device to separate out lumps and foreign matter. Sifting is done by shaking the flour through a sieve or strainer with small holes, which helps to break up any clumps and make the flour light and airy. This process also helps to remove any unwanted particles, such as insects or stones, that may have been mixed in with the flour.