FindFit
FindFit[data, expr, params, vars] finds parameter values that make expr best fit the data.
Examples
Fit data to a nonlinear model:
data = Table[{x, 3 Exp[-0.5 x] + RandomReal[0.1]}, {x, 0, 5, 0.5}]
(* Fit exponential decay *)
FindFit[data, a Exp[-b x], {a, b}, x]
(* {a -> 3.02, b -> 0.498} *)
(* Use the result *)
model = a Exp[-b x] /. %Please visit the official Wolfram Language Reference for more details.