Line feeding father's mother vital fluid (6)
I believe the answer is:
plasma
'vital fluid' is the definition.
'plasma' can be an answer for 'fluid' (plasma is a kind of fluid). I'm not sure about the 'vital' bit.
'line feeding father's mother' is the wordplay.
'line' becomes 'l'.
'feeding' indicates putting letters inside.
'father's' becomes 'pas' (pa can mean dad or father).
'mother' becomes 'ma' (Ma is another word for mother or mum).
'l' placed inside 'pas' is 'plas'.
'plas'+'ma'='PLASMA'
Can you help me to learn more?
(Other definitions for plasma that I've seen before include "Clear part of blood" , "Blood component and type of television" , "The watery part of the blood" , "part of donor's contribution?" , "Clear fluid portion of blood" .)