How do i know when to change the clutch in my car?

sometimes it kicks out of a gear, and sometimes i go to shift and it makes a nasty gringing noise when the cluch is pushed and trying to shift into gear
How do i know when to change the clutch in my car?
That sounds less like a clutch problem and more like a transmission issue (bent forks or such inside). Clutches just slip when they need replacing due to wear or spring weakening.
How do i know when to change the clutch in my car?
If you don't know you better take it to a technician. Those symptoms aren't nessesarily caused by a bad clutch.
It looks like you need a new clutch and throw out bearing. it make the grinding noise because of the clutch plate being wore out and you are not able to push it (the clutch) far enough. good luck