Line of punctuation initially helps you write about Henry (6)
I believe the answer is:
hyphen
'line of punctuation' is the definition.
'hyphen' can be an answer for 'punctuation' (hyphen is a kind of punctuation). I am unsure of the 'line of' bit.
'initially helps you write about henry' is the wordplay.
'initially' indicates taking the first letters.
'write' becomes 'pen' (synonyms).
'about' is an insertion indicator.
'henry' becomes 'H' (symbol for the unit of electrical inductance).
The first letters of 'helps you' is 'hy'.
'pen' placed around 'h' is 'phen'.
'hy'+'phen'='HYPHEN'
Can you help me to learn more?
(Other definitions for hyphen that I've seen before include "Sign linking words" , "Mark joining two words" , "It joins two words" , "Sign joining words" , "A horizontal word-joiner" .)