I’ll give it a go to try and explain from my own understanding of how it works…
With bitcoin or other more classic blockchains, there are nodes that are responsible for authorizing a transaction. Multiple nodes need to authorize a transaction before it becomes permanent in the blockchain.
In IOTA however, every device (wallet address) needs to authorize two other transactions in the tangle before it can send a transaction itself. This means that there is no need for nodes because actually every wallet acts as a node. Another consequence of this is that the more transactions happen, the quicker transactions are authorized.
Currently there is still the “Coordinator” in the tangle, which is a temporary sort of supernode that guards over the tangle’s integrity. With time and as the tangle becomes bigger and with more transactions, they will take these “training wheels” off. My personal interpretation is that the Coordinator is in place to prevent attacks on the network. When IOTA becomes big enough, the amount of wallets and transactions in the tangle will make it quasi impossible to attack the tangle with malicious wallets/devices because it would take millions of those devices to do so.