The claim feature allows you to use the funds you have in your Margin Wallet to settle a leveraged position as an exchange buy or sale.
So when you claim the position, you will be credited the sale size in USD (for a BTCUSD short), i.e. charged the base price multiplied by the size of the position (sale size of the position), or the buy size in BTC (for a BTCUSD buy), with a fee based on the amount credited.
For example, let’s say you have $100 USD in your wallet with 0.1 BTCUSD active long position. Claiming your position would use your available USD to reimburse the margin funding used to fund the underlying 0.1 btc at the opening price value and deduct it from your trading balance. So, at $250 base price, you will end up with ~$75 USD and 0.1 btc.
You will be charged the pending margin funding returns and the position amount in BTC, LTC, ETH, or ETC will be charged to your balance directly.
Claiming your position does not involve trading. If you don't have enough balance to claim the position when you click on "Claim", the system will tell you "You need to sell approximately XX Bitcoins at the current price to claim the position", but it's up to you to sell those Bitcoins with the type of orders you want.