Plotting observations to form equation

Hello. This is my first time with this website. Please let me know if this topic should have been placed in another forum group.

I have a set of observed numerical data. It is composed of lots of x,y coordinates. I can create a graph and the data forms a curved line. I would like to know how to enter the data into my HP 48GX (or a computer program?) so it can analize the curve and give me the equation that it represents. So I can take x and the equation will calculate y. I don't know if any graphing calculator can even do that. I have the User's Guied and the Advanced User's Manual, but I'm not even sure what terminology to refer to. Arrays? Matrices? It's been a while since I was in school and I'm getting back into math. Any comments or help in pointing me in the right direction would help.

Thanks!