The words yore, you're, your sound the same but have different meanings and spellings. Why do yore, you're, your sound the same even though they are completely different words?
The answer is simple: yore, you're, your are homophones of the English language.
Time long past: days of yore.
Contraction of you are.
Used as a modifier before a noun: your boots; your accomplishments.
A person's; one's: The light switch is on your right.
Informal Used with little or no sense of possession to indicate a type familiar to the listener: your basic three-story frame house.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.