A VST plug-in is an audio processing component that is utilized within
a host application. This host application provides the audio or/and
event streams that are processed by the plug-in's code. Generally
speaking, a VST plug-in can take a stream of audio data, apply a
process to the audio, and return the result to the host application.
A VST Plug-in performs its process normally using the processor of the
computer. The audio stream is broken down into a series of blocks. The
host supplies the blocks in sequence. The host and its current
environment control the block-size. The VST Plug-in maintains the
status of all its own parameters relating to the running process: The
host does not maintain any information about what the Plug-in did with
the last block of data it processed.

From the host application's point of view, a VST plug-in is a black box
with an arbitrary number of inputs, outputs (Event (MIDI) or Audio),
and associated parameters. The host needs no implicit knowledge of the
plug-in's process to be able to use it. The Plug-in process can use
whatever parameters it wishes, internally to the process, but depending
on the capabilities of the host, it can allow the changes to user
parameters to be automated by the host.

Details on how to use are found at www.steinberg.net/sdklicenses_vst3