How to cut lines into sides of hair?

I want to cut my sons hair and he wants two lines on the sides of his head. What do I use to do it and how?
How to cut lines into sides of hair?
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How to cut lines into sides of hair?
One of my friends always does it.


He said that you just need to cut the particular places with a straight line and you can see.


But remember, don%26#039;t cut the hair around the line, because by then it would make no difference to makes those two lines notable.