Helper is following animal with brown tail in forest (9)
I believe the answer is:
assistant
'helper' is the definition.
(I know that helper can be written as assistant)
'following animal with brown tail in forest' is the wordplay.
'following animal with' becomes 'assis' (I can't explain this - if you can you should give a lot more credence to this answer).
'brown' becomes 'tan' (tan is a kind of brown).
'tail in' says to take the final letters.
The final letter of 'forest' is 't'.
'assis'+'tan'+'t'='ASSISTANT'
'is' is the link.
Can you help me to learn more?
(Other definitions for assistant that I've seen before include "Aide, helper" , "second" , "Deputy, subordinate" , "One helping" , "one helps out" .)