The experience of futures trading on Spin is quite similar to centralized exchanges. Still, for a few minor differentiators. Long story short, here's a quick lifespan of your futures trade on Spin:
If you don't yet have a NEAR wallet, please check the wallet creation instructions in the Spot Trading section.
Connect your NEAR wallet to Spin.
Deposit funds to a Margin Account (which is a smart contract). In the blockchain, all users' funds on margin accounts are placed in a vault, where each transfer is assigned a number to indicate the owner of funds.
Create a futures position by choosing the order type and direction and position size (the leverage will be adjusted).
The margin ratio for this position is temporarily locked on your account (the margin ratio size depends on the position size and asset volatility).
Closing or changing your position results in the funds being settled and unrealized PnL and funding amounts are either added to or deducted from your margin account balance.
Withdraw returns from the Margin Account to your wallet.
Note that if you have an open position and want to withdraw funds to your wallet, you can easily do that, but the margin ratio will be reduced. If you suffer losses for this position, there will be not enough funds in your account for keeping the margin ratio above 0.7 and it will lead to liquidation.
To have a deeper understanding of Perpetual Futures and their implementation on Spin, please read the information provided in the Perpetuals section.