The Plex Media Server has various options that you can set from Plex Web App. The default settings are usually good enough for most installations, so you probably won't need to make many changes.
To change the settings, you first need to select the Server and then the Server Settings:
- From anywhere in Plex Web App, click to access Settings
- Click Server
- If there are several Servers on your network, select the one to manage using the drop-down on the left
On the left side, you'll see a number of settings categories:
Choose a category to access those settings.