How do I spot myself or other contacts on HAMRS windows version?
HAMRS just displays the spots for you. To spot yourself or another ham, you need to visit the POTA.app web site, log in, and spot from their site.
The biggest advantage to having the spots in HAMRS is the ability to import a spot to your log.
For what it’s worth, based on comments relative to a software package released by another developer, the POTA program leadership discourages completely duplicating the POTA.app spotting functionality into a stand-alone software package.