how to get power spectral density from time domain function by using fft

sir, i have the time domain series values i.e,x vs t from experimental data of a lithium ion battery on which random vibration were said to be induced on a battery,but i don't know how to convert that time domain series to frequency domain function i.e PSD from fft in matlab. Sir,please could you help me out with the help of any syntax.

Answer 1

[Star Strider]

See Power Spectral Density Estimates Using FFT and the R2015a documentation for fft.