If you are requesting instruction on generalized techniques for computing regressions and/or best-fit equations for various different types of relations and/or graphs, then this is well beyond what we can provide here.
You might want to consider hiring a tutor, local to your area. In face-to-face meetings, the tutor can see the pictures you are looking at, review your text to see the formulas and/or techniques you've been taught, and can step you through the process. A few hours a week should serve to get you caught up.
Eliz.