‘Your’ is the second person possessive adjective, or, in simpler terms, it is used to describe something as belonging to you. It is nearly always followed by a noun. For example,

• - Is this your wallet?
• - Your presence at the table is very much appreciated.
• - What happened to your foot?

‘You're’ is the contraction of ‘you are’ and is often followed by the present participle, ie, verb form ending in ‘ing’. For example,

• - You’re looking ill.
• - You’re going to be late.
• - You’re a fool.