What a transaction actually is

A transaction is a signed instruction: “from this address, do this.” The network checks the signature, then applies it.

Try it

One tap. Maya signs, the network waits, Jules’s bag changes.

Maya

Sender

4.000 ETH

Jules

Recipient

1.200 ETH

Suppose Maya wants to send 0.5 ETH to Jules. Her wallet builds a small packet: the destination, the amount, a fee, and a counter (the nonce) so the same payment cannot be replayed. Then it signs the packet with her private key. The raw key never leaves the wallet.

That signed packet is broadcast to the network. It sits in a waiting room called the mempool until a validator includes it in a block. Once the block is accepted, Maya's balance is down 0.5 ETH plus the fee, and Jules's is up 0.5 ETH. Everyone's copy of the ledger matches.

Until it is in a block, the payment is only a proposal. After it is in a block, reversing it would mean convincing the network to throw away that block and everything after it — which, on a healthy chain, does not happen because you asked politely.

Transactions can also carry data: “call this contract, with these arguments.” Sending ETH is the simplest case of a more general idea: a signed change request.

Try it

Paste a mainnet hash, or load a canned one. This is the same public data Etherscan shows.

Takeaway
You do not “upload coins.” You publish a signed instruction, and the network updates the shared ledger.

ETH