Farther means more distance. It is used to measure the way / path.
America is farther from Bangladesh than Pakistan.
Rajshahi is farther from Dhaka than Natore.
I live farther from you than him.
He will go farther from here than her.
Further means additional or excess.
You will not come here further.
I wanted further help from him.
His friend will not give him further any money.
Much, Many, Many a, A great many.
Much means more and it is used in the singular number. It is used with a view to indicate quantity
There is much water in the glass.
I have much money.
He has spent much time to do it.
I want to earn much money in this way.
Many refers also more and is used with countable nouns and plural number.
I have many friends in my area.
Many people gathered there to join the party.
There are many girls in our class.
Many people can’t get food but we waste much food.
Many a means same as many but it is used with singular number.
I have many a book.
He had many a friend.
You made many a mistake.
A great many refers to many also and is used with plural number.
A great many people joined the party.
A great many students came to college today.
I saw a great many boys playing in the field.