I am not able to do some functions on my TI-84

To have the coefficient correlation show up when you calculate a regression, you must first turn diagnostics on.

The way to do this is press 2nd then zero. You are now in the catalog. Go to the d's in the alaphbetic list, highlight "diagnostic on" and press enter. You will be taken back to the home screen press enter and you get the word "done". The diagnostic is not on unless you get the word "done".

Now when you calculate a regression, the correlation coefficient will show up. It is designated as r = on the home screen.