A player with ten or more poison counters loses the game. This is a state-based action and doesn't use the stack. In other words, it happens immediately and players can't respond to it, just like a player losing the game due to having 0 or less life.

Any enters-the-battlefield abilities of the copied creature will trigger when the token enters the battlefield. Any "as [this creature] enters the battlefield" or "[this creature] enters the battlefield with" abilities of the creature will also work.

Any other effects of that damage, such as life gain from lifelink, still apply.

Conversely, replacement effects that apply to the number of counters put on a player can modify the counters placed this way. For example, Vorinclex, Monstrous Raider's last two abilities can apply to counters placed this way.

Damage dealt by a creature with toxic grants the same number of counters regardless of how much damage is dealt. Notably, if a replacement effect modifies the damage in some way (such as that of Gratuitous Violence), the number of counters given remains unchanged.

Except for the listed exceptions, the token copies exactly what was printed on the original creature and nothing else (unless that creature is copying something else; see below). It doesn't copy whether that creature was tapped or untapped, whether it had any counters on it or Auras or Equipment attached to it, or any non-copy effects that had changed its power, toughness, types, color, or so on.

If a creature with toxic deals combat damage to a creature or planeswalker, or if it deals noncombat damage, toxic has no effect and no player gets poison counters.

If something becomes a copy of the token, the copy also has base power and toughness 1/1 and has toxic 1.

If the copied creature had {X} in its mana cost, X is 0.

If the copied creature was copying something else, then the token enters the battlefield as whatever that creature copied, with the exceptions noted above.

If the token is a copy of a creature whose power and toughness are defined by an ability (usually printed as */* or similar), the token doesn't copy the ability that defines its power and toughness. It remains a 1/1 creature.

Multiple instances of toxic are cumulative. For example, if a creature has toxic 2 and gains toxic 1 due to another effect, combat damage that creature deals to a player will cause that player to get 3 poison counters.

The token copies the creature as it last existed on the battlefield before it died, not as it existed in the graveyard before it was exiled.

Toxic doesn't change the amount of combat damage a creature deals. For example, if a 2/2 creature with toxic 1 deals combat damage to a player, that creature will deal 2 damage. The results of that damage are the player loses 2 life and gets a poison counter.