Steem is a blockchain, a distributed ledger on the internet. It has a native cryptocurrency called STEEM it uses to pay as rewards for posts. The rewards are determined by stake-based user votes during a seven-day voting window. (The users are in control, not some giant corporation!) STEEM can be exchanged for fiat on a number of cryptocurrency exchanges around the world. Or it can be staked giving you influence over the payouts. Half of your rewards will be paid out in staked tokens called Steem Power anyway (they can be powered down and sold). Steem offers you ownership over your experience in in the sense that there is no single centralized entity that can take down, shadow ban or demonetize your content at will. Steem Power not only gives you influence over rewards but also an ability to take part in the governance of the platform. You need a small amount of it to use the blockchain but only a couple of dollars worth is enough. Or you can get it for free by having Steemit, Inc (the company that develops the blockchain) delegate some of it to you when you sign up at their site for free. Another option is to have an app onboard you by offering you a guest account.
Yet another is to have a Steemian like myself with bunch of account creation tokens in store to onboard you for free and delegate a bit of Steem Power to you until you have earned enough to transact on your own Steem Power.