"Farther" refers to physical distance. "Further" relates to metaphorical or non-physical distance. Ex.: The park is farther than I thought. We need to look further into this issue.

"LED" and "LEAD"

"Led" is the past tense of the verb "to lead." "Lead" can be a verb meaning to guide or a noun referring to a type of metal. Ex.: She led the team to victory. He will lead the project. The pipes are made of lead.