"Free spins" are simply spins of a slot that are conducted for free, as in free of charge to your Chips account. They can be offered as a bonus for certain actions such as logging into the site, completing deposits, or playing certain (meta) games - or even specific slots indicated by the site. Using free spins, you can earn winnings that are accredited to your player account. Sometimes, winnings from free spins come with certain conditions, e.g. a maximum withdrawal amount or a stipulation that they can only be withdrawn once a monetary deposit has been made. You're best advised to know the terms and conditions of free spins before making use of them.