Tackle area: Keep them on the floor until the referee tells you to move (at which point you get straight off, as any further interference with the player can be penalised be the ref) - it allows your defence to set properly. Two "markers" go in on defence as well, and stand directly in front of the attacking player who just got tackled - they have to be directly in front,otherwise a penalty can be given for "markers not square".
Play the ball: Roll it backwards but make sure you make contact with your foot. You don't have to put the ball down and then roll it with your foot (though could be easier to start with), but some form of contact is needed (if you watch pro players they start rolling it as they stand up and basically brush it with their foot) - it's a penalty if you don't so it's important to remember.
Lineouts are basically a quick tap penalty - If it's kicked out then someone on the non-kicking-side (i.e. whose lineout it is) gets the ball and passses it to a player on the pitch (so like a quick lineout). They then take a quick tap penalty (usually tap it and then pass it to a prop who is running on to it at pace). If there has been a 40/20 kick (kicked from behind your 40m and bounces out over their 20m) it's a scrum awarded to the kicking team.
Another thing that some union players forget (and league players remember too well when crossing over) is that you can throw the ball over your own deadball line and it's a goal line dropout to your team. It's also a goal line dropout if you carry the ball in to your try area and you ground it/are tackled, and if the ball is kicked and it bounces in to the in goal area and you catch it and are tackled. If you catch the ball on the full in your in goal it's a 20m restart (quick tap on the 20m line).
There's a few bits and bobs to get your head round, but it all falls in to place eventually.