The address of the online version of Plex Web is https://app.plex.tv/desktop – however that won’t be of much help if your server itself isn’t working properly.
Did you actually get through the installation wizard at first run or are you stuck even before that? Can you please briefly describe what steps you did while installing the server.
Also… how are you currently trying to access the server locally? – e.g. https://127.0.0.1:32400/web (if the server is running on the machine you’re working on) or https://your-plex-media-server-ip-address:32400/web
I ran the installer and followed defaults. That went without incident, no errors or anything. It opened minimized to the system tray. I told it to open the server, it asked for my login, accepted it, and reloaded with the Plex logo where it sits and nothing changes. I haven’t been able to get any further to set up libraries or anything. I hope that answers your questions and thank you for the prompt reply.
11-25-18 Update.
My laptop ran updates today and when it restarted, the library automatically started the creation process. So, I don’t know what fixed whatever the issues were, but its fixed now.