It lets a writer get rid of unwanted characters (6)
I believe the answer is:
eraser
'it lets a writer' is the definition.
The definition suggests a singular noun which matches the answer.
'get rid of unwanted characters' is the wordplay.
'get rid of' becomes 'erase' (I've seen this in another clue).
'unwanted characters' becomes 'r' (I can't explain this - if you can you should believe this answer much more).
'erase'+'r'='ERASER'
Can you help me to learn more?
(Other definitions for eraser that I've seen before include "correction device" , "India rubber" , "Rubs out" , "Item used for rubbing out" , "Correcting implement used in drawing or writing" .)