You send them to the bridge's vault (its lock account), with a flat fee in XRP. Xaman signs both at once; another wallet pays the fee first, then the tokens.
2
The operators check it
Each of the bridge's operators checks the payment on the XRP Ledger. Once enough of them agree, they approve it.
3
Your tokens arrive
The same amount is created on XRPL EVM, in your wallet.