(adjective) at a greater distance
(When related to physical distance, farther is a synonym)
It was much further to the town centre than I remembered.
(adjective or adverb) more or extra (unrelated to physical distance)
Have you anything further to add?
If you have any further problems, let me know.
We need to talk further about this.
(verb) to develop or make progress in something
Additional training is probably the best way to further your career these days.