Poloniex lost their top-notch position among crypto exchanges to Bittrex and then Binance. You are right that Binance has one of the best trading fees for spot or margin tradings.

They also have many promotions and lottery events for their users. They have a Binance Academy

It is the guide for Margin tradings on Binance Binance Margin Trading Guide and you can find many other documents for your trading life from the academy.

You have to spend time to get familiar with a new platform you are using and then all things will be fine.