This may help:
If you’re tackled - as in grounded and held - you can pass the ball if you’re able to do so “straight away”. Or if the try-line is within reach, without needing to move your body, you can reach out and ground the ball “straight away”. Otherwise you must let go of the ball and something similar to a scrum takes place, except that it’s not a set-piece but an impromptu affair for whoever feels like joining in. For anyone who doesn’t, they must retreat to their own side of the “ruck”, as it’s called. Getting quick ball from a ruck (i.e. from a ruck that lasted for only a few seconds) is a powerful attacking weapon as defenders who couldn’t get back behind the ruck are temporarily “offside” and can’t interfere with play even after the ruck is over. Because of this, defenders may try illegally to prevent the ball coming out, and can be severely punished for it.
If you’re grabbed but not grounded, players from either side may join in the resulting “maul”, which is like a ruck but with the ball carried. Again, anyone not in the maul must retreat behind it to their own side. Once the maul’s in being - the ball-carrier plus at least one player from each side all scrapping for it - there is no longer a “tackle” situation, and bringing down the ball-carrier is illegal (“a maul ends a tackle”) until he quits the maul or the ball is released from it. However, if you can get the ball away from him, you’re at liberty to do so.
Rugby league (RL) looks a little more like American football, in that a tackle ends the current play and the player with the ball must replay it in what RL laughingly calls a “ruck”, in which everyone lets him go, he places the ball on the ground and rolls it back with his foot, and play continues. But on the sixth tackle, the ball is turned over to the opposition. (It’s always “nth and goal” in RL).
Hope this helps.