It's a scam, ignore it or use "Report spam".
Of course the usual rules apply to stuff like this:
1. You can't win what you didn't enter.
2. You can't win what doesn't exist (if Google was giving money/items away there would be legitimate news stories about it).
3. You can't be one of hundreds of identical winners (searching finds many other posts about the same type of prize).
4. If an announcement says it’s from Google but didn’t come from @google.com, then it’s not really from Google.
5. If it sounds too good to be true, it is - run away.