Docs Your account
Deposits, withdrawals and transfers
Move USDC in from Arbitrum, out again, and between Hyperliquid's balances, from one dialog.
Your address at the top right is a menu. Deposit, Withdraw and Transfer open one dialog with three tabs.

Deposit
Sends USDC on Arbitrum from your wallet to Hyperliquid’s bridge; it reaches your Hyperliquid account in under a minute. Hyperliquid credits nothing under 5 USDC. You need a little ETH on Arbitrum for the transfer.
Withdraw
One signature on Hyperliquid, no gas. USDC goes to the same address on Arbitrum in a few minutes; Afterbell can never send it anywhere else. Hyperliquid takes its own small withdrawal fee.
Spot and perps
Your account keeps spot and perps balances apart, and perps margin comes from the perps balance. Move USDC from spot to perps, or back, with one signature.
The stock exchanges
Stock perps on xyz, EntropyIO or Paragon keep their own margin. If your account is in Hyperliquid’s unified mode it draws from the main balance on its own; otherwise the ticket offers Move USDC when a stock order needs more margin than that exchange holds, and the portfolio moves it between exchanges any time.