some vi equivalents please?

[rustom]

1. In vi I can delete a line that contains a <pat> with
:g/<pat>/d

How is this done in emacs?

2. match-variables:
If I want to remove everything after the second : (in a file that has
3 fields separated with two :'s)
I do
:s/\(.*\):\(.*\):.*/\1 \2
How do I do that in emacs?

Thanks