Germany just began any serious action, and there is a 2 week lag before seeing any sort of impact.
In Poland we had a national lockdown a week ago (which you can see everywhere - empty streets and so on), and so far the numbers don’t reflect it at all.
As for locking people down, yes you can do it, it’s called a quarantine.
So I would expect to see first effects in new infection numbers over the coming week, with nearly full effect probably visible some time during the following one.
Most might have stayed at home but the 5% that didn't are still enough to spread it exponentially.
Home office has changed from being the exception to being the norm for a week now at my workplace (an IT company), and I've heard the same from members of my family working elsewhere (in non-IT businesses).