A message say that i have to open the site into the sandbox, but I don t konw how.
This isn’t a message that I’m familiar with in avast !
What version of avast of you have, free/pro/ais ?
Avast may well ask/recommend that you open a browser or a file/application in the sandbox but not a website.
Try to replicate what it was that gave this message and make not of all of the information. Or take a screenshot of the message window and attach to your next post.