You need to select a range on the Y-Axis to observe. SpikeRecorder automatically spike-sorts when you open up the analysis on a recording. 

Adding a spiketrain - first image is an example of a selected spike train. Second image is what it looks like prior to selecting your range. Drag the pointer icons to select the range. The plus button can add new spike trains for comparison.

Lastly once you have selected the spike trains, arrow in bottom left hand corner will pop up the analysis/comparative charts.