Can I meet with friends or sit with neighbours on my driveway if we stay 2 metres apart? 

Contact with people outside of your bubble needs to be limited to reduce the risk of transmission. You can have a quick chat with your neighbours if you are outdoors and 2 metres apart.  

What if I’m somewhere that’s really crowded? 

You should avoid places where it’s difficult to keep your 2 metres distance. If a public space becomes too crowded to maintain 2 metres you should consider leaving. People should not be congregating at Level 3, and no gatherings are allowed, except under very limited circumstances.