Trading futures

Hi, I have few questions about Binance Futures.

1. When i open limit order on futures and confirm it order appears in the "open positions"- why is that ?
2. Why sometimes the final cost of limit order is less then the order itself ?
3. Why sometimes when i try to open limit order "order fee" is so high ?

PS. I am trading on binance futures perpetual USD-M

Thanks to everyone who will answer that, im quite new to futures trading and need help :)