n-fold convolution of a probability function

Question

I have few questions about convolutions.

1. I have a sample data sheet in the form of $x$ vs $f(x)$. [discrete points]

Now I want to do $3-$fold convolution of $f(x)$ and plot the 3-fold convoluted functions w.r.t $x$. How to do it?

2. suppose length of $f(x)$ is $10$. So, length of $x$ is also $10$. After $2-$fold convolution (i.e $f_2(x)=f(x)* f(x)$), length of $f_2(x)$ will be $19$, but original length of $x$ is still $10$. Then how to plot $f_2(x)$ w.r.t $x$?

Kindly give some suggestion.