Nifty futures and intraday share prices - what is the relation?

If say i want to do intraday trade on ICICI BANK Shares, So i noticed sum people also have/monitor live price of "Futures" of ICICI Bank Prices...

So what is co-relation between the future prices of tht particular share to its current prices ? How does monitoring F&O prices of an particular share affect its current prices in intraday tarde?

My second question,
What is the relation between monitoring afterhours numbers/prices and live current share prices ?

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