Simply install your VST in a defined folder.
Then read the manual : https://s1manual.presonus.com/Content/Setup_Topics/Managing_Your_Content.htm?Highlight=vst
When Studio One starts for the first time, most of your plug-ins are located automatically and are ready to use immediately. If Studio One fails to find certain plug-ins, adding them is easy.
To add any missing VST plug-ins, navigate to the Studio One/Options/Locations/VST Plug-ins (Mac OS X: Preferences/Locations/VST Plug-ins) menu and click on the [Add...] button, then specify a location and click OK. You can also drag-and-drop any folder from the Explorer/Finder into the Locations list. Studio One then scans these locations at startup, including searching for new plug-ins you’ve added. You can always add more locations if needed.
AU, VST 3, and ReWire-enabled plug-ins and applications have their own pre-set file path in the OS and do not have to be located manually
Then for using your VST, simply read this : https://s1manual.presonus.com/Content/Recording_Topics/Instrument_Tracks.htm?Highlight=vst
Hope this help.