while checking the value the condition comes like this if certain cell contains no value (what symbol or command has to be used to specify that cell contain nothing) then insert the value contained in
another cell. how to specify this in nested if statement

This doesn't sound like a Nested IF, it sounds like a basic IF function. You also didn't tell us what to return if the "certain cell" isn't empty
Let's assume your "certain cell" is A1. Try this:
=IF(A1="", B1, "The cell isn't empty")
A Nested IF would contain another IF:
=IF(A1="", B1, IF(A1>100, C1, A1))
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