Trying to transform data into FFT format

I have been trying to convert data into FFT format, but it does not look like a wave in the graph. The columns I am calling to match the first plotted diagram. The data does not look like a wave up close as it should. I am assuming that is the problem.

%T = xlsread('Baseline.xlsx');
t = T(:,1);
x_t = T(:,5);
t=t-t(1);
plot(t,x_t);

S = [t,x_t]
X = fft(S)
plot(X)

[Walter Roberson]

Why are you taking a fourier transform of your time variable? Why does your time variable have duplicate values? Why does the other column contain nan or inf?

[Mason Condren]

From muy understanding the fft command is for a function. I only have data. So, I

converted the data into a 2x* matrix to FFT it. I do not have a good understanding of the command when it comes to raw data.