What does Ethereum's blockchain looks like? Are there only transactions of the states' changes, or are the accounts in every block?
The transactions and their input data, and block header information such as the hash of the previous block and miner who mined it.
This is probably too much information all once. This block explorer lets you look around.
block 5,454,817: https://etherscan.io/block/5454817
There's a header and 198 transactions. The "state" is not included in every block since the bandwidth would be crushing. There's no need for it since each node can compute the state independently based on the transactions it sees.
Hope it helps.
To get a more visual view, you can head over to ethviewer, and here's a snap of it.
The dots are transactions. These transactions are validated and included in blocks by miners. Transaction contain information of
As said by @rob-hitchens states are not included in the block. The current state can be calculated on the basis of transactions and ethereum client which connects to the blockchain, does this thing for you and provides latest information.