Flask, Django, NodeJS on Vesta Panel
You will have to build them from source yourself or use binaries.
If you build them you will probably need to pass user directory parameters to the build, e.g.: you will have to crete "/opt", "/lib", "/tmp" and other root folders and point the build to them.
Else just place the binaries in the /bin folder, create it if it doesn't exist, add it to your $PATH and use them directly.
How to run flask (A Python Microframework) on Vesta Panel?
It's not specialized question for Flask. I'm asking django, flask, cherrypy, sanic, nodejs, strongloop etc.
It's looks like basic question but vesta panel wrote with PHP and using apache, nginx. It's complicated. Python and NodeJS using their own socket.