With nomenclature, it's always best to break down the name & tackle it one part at a time.
"4-nonene" "non" = chain with 9 carbons "ene" = there's a double bond somewhere "4" = signifies the location of the functional group, which is the double bond.
So, draw a 9 carbon chain. Number each carbon. Draw a line between carbons 4 & 5 to mark the double bond. That should do the trick.
Remember to divide and conquer. Also do practice questions to get the hang of it.
