For example, stock index futures are SSE 50 stock index futures, CSI 500 stock index futures and CSI 300 stock index futures. They just have different goals.
Stock index futures is a kind of financial futures. The threshold is the limit of 500,000 funds.
As for the choice of contract, it is usually to choose varieties with large positions and large turnover. This will be more liquid.
If you have any questions, please feel free to ask me.