Development groups or companies decide to implement airdrop tokens to attract attention in the ICO to encourage investment in their tokens. They are also often used when launching a new currency to make good deals, making people excited, and attracting more customers. When Facebook recently introduced a new advertising policy that explicitly banned the ICO, many switched to airdrop advertising as an alternative to PPC advertising.
Normally what needs to be done is clearly noticeable before the airdrop (after all, is still to split the coin). You may also be required to follow on Twitter or join a Telegram group. Make sure you do these and do not give up the track or walk away before airdrop, otherwise you might miss out.