Please give me an API key

You do not need to ask for a public API key, in order to get one you just have to register in VirusTotal Community (top right hand side of VirusTotal). Once registered, sign in into your account and you will find your public API in the corresponding menu item under your user name.

Or visit https://www.virustotal.com/gui/my-apikey

In this page you can find your apikey string: