Need help with FFT of a .csv

Hi! I have a .csv file of a rectangle pulse and I need to turn it into the frequency domain and plot it, but i dont know how to use the fft command. I'm using this code to plot the file

if true
  % code
clc, clear all, close all
M=csvread('Cuadrada.csv');        %Lectura del .csv
tiempo=M(:,1);                    %Vector Tiempo del .csv
Voltaje=M(:,2);                   %Vector Amplitud del .csv
subplot(2,1,1)
plot(tiempo,Voltaje)              %Gráfico de datos del .csv
title('Señal en Tiempo')
xlabel('Tiempo (s)')
ylabel('Amplitud')

end

Heres the output:

Answer 1

[dpb]

There's example of PSD at

doc fft  % illustrates computation and how to get the frequency