Query Abt How to invest

In old videos with Finance with sharan, Video on Credit Cards Aly is saying use Cashback as Investment. How does that work? Say example, i Have spent 3k from my credit card and say1.5k is casback. Now this cashback debits to creditcard right, then now again should i debit this 1.5k and invest it or how does that work…I am unable to understand.

Stop watching Sharan Video and start reading Varsity

who is sharan?