To expand on what flaze said, "your" is a possessive adjective, so it is always used with a noun: your house, your cat, etc. "Yours" is a possessive pronoun, which replaces the noun: This is my book, that is yours. In this case "yours" replaces "your book". This website gives a good explanation: http://web2.uvcs.uvic.ca/elc/studyzone/330/grammar/poss.htm

1. This is MY pen. So it's MINE. 2. This is YOUR car. So it's YOURS. 3. This is HIS phone. So it's HIS. 4. This is HER hat. So it's HERS. 5. This is OUR country. So it's OURS. 6. This is THEIR house. So it's THEIRS.

'your' is a possessive adjective. E.g. 'It's YOUR pen' 'yours' is a possessive pronoun. E.g. 'It's YOURS.'

"your" is a subject. "yours" is a own.

I'm glad that you have asked this question,because if you confuse them it will make you look dump.