1: what is the different between spot trading and futures trading.
Spot trading involves buying or selling of an asset at the current price of the market. It's meant to be an instant delivery or on the "spot". While futures is a form of derivatives contract to sell/buy an asset at a specified future date.
between Stop Limit or Stop Loss and
OCO or order cancel order which is the safest for trading.
Depends on your strategy.
Investopedia states it well
Stop-loss and stop-limit orders can provide different types of protection for both long and short investors. Stop-loss orders guarantee execution, while stop-limit orders guarantee the price.
OCO is a conditional order that good if you are not so much around the trading charts or terminal
4: between spot trading and futures trading which is highly risk and highly reward that uses leverages.
Obviously Futures trading is highly risky and rewarding, It depends on how good or lucky you are.