I think that I understand that if I parameterize $y=x\,$ I can write it as $f(t)=(t,t)\,$. So I'm assigning position vectors (coming from the origin) to the point $(t_0,t_0)$ for $t=t_0$. So I can say that that a vector valued function takes a scalar parameter and assign to a vector in $R^n$. And if a $(x,y)$ is going from $R^2$ to $R^n$, it is a vector field, because for each position vector I'm associating a vector ? (instead of each scalar $t$)
I'm confused because if vector valued functions can be going from $R^2$ to $R^2$ isn't it just like a vector field? (for each vector position I receive another vector in that point).