Which unsubscribed version of Studio One 5 are you using? If it's Artist or Professional you should be able to get those options [goto Studio One > Options > Locations > VST Plugins and add their locations. If they are effects you can then access them from the "+" next to "inserts" on the top of the mixer faders. If they're instruments click on 'browse '(on the bottom right) > 'instruments', and drag it to the track you want]. But Studio One Prime on the otherhand does not offer VST usage, so with that version you wouldn't have those options.
