If you have many trials with a baseline of 1 second for each trial, you can compute the FFT of each 1s block and average them (something similar to what the PSD process does on continuous signals). You can do this by dropping all your imported trials in the Process1 box, and run the process "Frequency > Fourier transform (FFT)" or "Frequency > Power spectrum density (Welch)": time window [-1s,0s], estimator > 1s, save average.
Both processes should give you the same results.
Standardize in what way?
To represent better the different frequency bands, you can use log-scale for either/and X and Y axis. You could also use the process "Extract > Extract values" to keep only a specific frequency band of interest.