The word "further" is often confused with the word "farther." Sometimes there is very little difference between the two words, so it’s not always a mistake to use one instead of the other; however, there are some differences:
You can use "further" (or "farther) when talking about an additional distance:
We need to go a little further to find a place to eat.
The weather is warmer further south.
Further north of here there are some great places to go camping.
Please move that chair a little further to the right.
The bike trail is further up the hill.
Notice that the word "further" is used in a way that is similar to the word "more."
There will be no further discussion regarding this matter.
Further progress has been made on the construction of the bridge.
Further economic growth is dependent on low interest rates.
Look no further. You have found what you were looking for.
One big difference between "further" and "farther" is that "further" can be used as a verb, but "farther" can not.
Joe would like to further his education by taking classes online.
Sarah is furthering her company’s interests by moving to Mexico.
The word "furthest" is a superlative form of the word "further," which is essentially a comparative adjective.
Furthest from my mind is going back to work when I’m on vacation.
Pluto was regarded as the planet in our solar system furthest from the sun until astronomers decided it was not really a planet but a dwarf planet.