I don't know how to set the nlinfit function

Hello! I have a function in 4 variables and I know the values of 14 points, but I need an analytical expression. I found the command nlinfit but it is asked to define a beta0 vector (initial guess of the coefficients) and I don't know in what form is the output function. So I don't know what to guess in beta0 and I don't know how to interpret the results (what do the coefficient represent). Thank you!

[Wayne King]

But you have to have a model in mind to even use nlinfit. You have to the form of the output function.