Put the vst file in program files/image line//fl studio/plugins/vst
once you've done that open fl studio..click on "channels" then click on "add one" and finally choose "more" from that menu
you will now get a list of all the default vsts fruity has so your gonna need to scan for the vst that u jus added, so click on "refresh" at the bottom and select "fast scan" your new vst should be added on that list now...simply double click on the name
hope that helped