These words are commonly confused in English, here you can se the difference between them

1. Farther and Further
The word farther isusuallyusedasan adverb. In American English,we
say farther when talkingabout a physical, measurable distance. For
example, “We run fartherthan we hadplanned.”
The word further has several meanings. It can be used as an adverb,
adjective, and even a verb. As an adverb, further means “to a greater
extent.” For example, “The scientists are looking further into the new
research.”

2. As an adjective, further means “more or additional.” For example,
“Furtherresearch is needed to reach a conclusion.” Notice how there is
no physical, measurable distance in these examples.

3. Further can alsobe averb.Initsverbform, it means“tohelpthe progress
of something.”Forexample, you might hope to “furtheryour career”by
learning English. In other words, you hope learning English will help
you advance your career. Again, there is no physical, measurable
distance.