TOPS Split just selects parts of the IW data product (kind of a subset) and Merge puts various products together. They are not related to segmentation in the sense of object oriented image anaysis.
An unsupervised cluster analysis can be done in Raster > Classification > Unsupervised
Image segmentation is also included in SNAP in the meanwile but I haven’t found a way to use it properly yet: Segmentation and Classification