You want the jubilee line, eastbound trains (you can catch them from Green Pk, Bond St, Baker st. etc). Make sure your train goes all the way to Stratford and doesn't stop at London Bridge.
Get off at Canning Town station and catch an eastbound DLR train to London City Airport or King George V.
For further reference, here is a comprehensive London underground map:
http://www.london-tube-map.co.uk/london-…
As for the O2: check out this link:
http://www.theo2.co.uk/location/transpor…
You can get either 1day or 7day travelcards:
1day travelcard covers all 6 zones and expires at midnight;
7day travelcard may be issued for zones 1, 1-2, 1-2-3-4, etc. Prices vary accordingly.They expires at midnight of the last day.
You are allowed on trains (both railway and tube), buses and night buses. Terravision buses do not belong to public transport and are not included.